A0-A087 656 NAVAL POSTGRADUATE SCHOOL MONTEREY CA F/S 4/1OPTICAL AEROSOL SPECTROMETERS FACTORS AFFECTING OPTICAL EXTINCT--ETC(U)APR 80 6 E SCHACHER, K L DAVIDSON

UNCLASSIFIED NPS-61-80-013

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NAVAL POSTGRADUATE SCHOOLMonterey, California

!0~~DTIC '

'\ AUG 81980

' C

OPTICAL AEROSOL SPECTROMETERS

FACTORS AFFECTING OPTICAL

EXTINCTION PREDICTIONS

G. E. Schacher and K. L. Davidson

Environmental Physics Group

and C. W. Fairall, BDM Corporation

April 1980

Approved for public release; distribution unlimitedPrepared for: Naval Ocean System Center

San Diego, California 92152

IS7 8098 7o006

NAVAL POSTGRADUATE SCHOOLMonterey, California

Rear Admiral J. J. Ekelund J. R. BorstingSuperintendent Provost

The work reported herein was supported in part by the CaliforniaAir Resources Board, Sacramento, California.

Reproduction of all or part of this report is authorized.

This report was prepared by

G. E. Schacher K. L. DavidsonProfessor of Physics Associate Professor of

Meteorology

C. QC. W. FairallBDM Corporation

Approved by: S

J. Dye7 Chairman .. J. Haltiner,ChairmanDepartment of Physics & Chemistry Department ofoy

William M. TollesDean of Research

.. ........ ! J .. . . *. 0 - . L . .. . . - . . . ..

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Approved for Public Release, Distr ibution Unlimited

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OSUPPLEMENTARY NOTES

I9. KEY WOROS (Cqmtitu. an w. revers ot 41owseeren Uto IEWE F &lookmim.

Aerosols, Aerosol Spectrometers, Optical Extinction

41.A"TOACT (CaneRO Od 011FN 01411 It M 1060M no e nd 1410001111 6V IMeh Moo"e

Optical aerosol Counters are used to measure aerosol spectraand thence to calculate the aerosol contribution of opticalextinction. This report contains the results of field experi-*1 ments and laboratory investigations of the performance of the NPSspectrometers. Areas of concern in the use of these spectro-meters and the subsequent calculations are identified and dis-cussed. In general the spectrometer performance I*aL uate forU8se in predicting thepromnef overoceanop Osvt-

00 , Un47 sotvio or 1 ev es Is o"016ET8S/R 0102-814-6401 q1AjX a

OPTICAL AEROSOL SPECTROMETERS FACTOR AFFECTINGOPTICAL EXTINCTION PREDICTIONS

by

G. E. Schacher, K. L. Davidson, and

C. W. Fairall

ABSTRACT

Optical aerosol counters are used to measure aerosol spectra

and thence to calculate the aerosol contribution of optical

extinction. This report contains the results of field experi-

ments and laboratory investigations of the performance of the NPS

spectrometers. Areas of concern in the use of these spectro-

meters and the subsequent calculations are identified and discussed.

In general the spectrometer performance is adequate for use in

predicting the performance of overocean optical systems.

Ac' -A u cn For

i--TdT . "

IIU

1 . . . _ _ - --- ,- -- -

OUTLINE

Page

I. Introduction 7

II. Equipment and Data Handling 9

III. San Nicolas Island Breaker Line 16

IV. San Diego Intercomparison 21

V. San Nicolas Island Intercomparison 23

VI. Calibrations at Mainz and Garmisch 35

A. Particle sizing--ambiguity zone effects 35

B. Bin edge shift 36

C. Particle density calibrations 43

D. Counting statistics 45

E. Spectrometer comparison 46

VII. CEWCOM-78 Comparisons 48

A. Ship and wind influence 49

B. Comparison with NOSC aircraft 53

C. Comparison with NPS optics 53

D. Comparison with Wells, Katz, Munn Model 54

E. Comparison with PMTC Optics 55

VIII. Extrapolation to Large Sizes 61

IX. CTQ-79 Comparison with NPS optics 82

X. Summary and Recommendations 88

2

List of Tables

Table 1. Sample data output for a one half hour averagingperiod. Listed are values of radius, dN/dr forthat radius, and the parameters of the 7th orderfit to the data.

Table 2. Calculated aerosol contributions to optical extinctionfor wavelengths of 0.53, 1.06, 3.75, and 10.59 um.Extinctions are in m-l.

Tables 3a-3g. Fractional aerosol contributions to opticalextinction for 9 wavelengths from 0.49 to 10.59 um.The fractional contributions from 25 size ranges arelisted. All data are for 5/15/78 - 2046 except whereindicated. The type of fit used for the extrapolationregion is indicated for each table.

a. 1646 polynomial extrapolationb. polynomial extrapolationc. linear extrapolationd. constant extrapolatione. cut offf. 5/8/78 - 0835, polynomial extrapolationg. 5/8/78 - 0835, linear extrapolation

Table 4. Calculated aerosol contribution to the optical extinctionat 0.488 Um and the percent contribution due toextrapolated sizes for various extrapolation techniques.

Table 5. Aerosol contribution to extinction as determined opticallyand from measured aerosol spectra.

3

Figure Captions

Figure 1. Spectrometer response vs particle radius for in-dices of refraction of 1.5 and 1.33 for ASASP andCSASP spectrometers. Shaded areas are ambiguityzones.

Figure 2. ASASP and CSASP spectrometer bin configurations.The bins for each range are shown as boxes. Binsfor which there is overlap are shown partiallyshaded. The size ranges for the ambiguity zonesfor each instrument are indicated by the shadedareas.

Figure 3. Comparison of data for various size bins. X-ASASPrange zero. 0-Bins for which there is range overlap.The data is from a one-half hour average during theSNI intercomparison experiment.

Figure 4. Location of shoal with respect to SNI and posi-tions at which aerosol data was taken abord theR/V ACANIA. Circled numbers are location of R/VACANIA aerosol measurements. M indicates themeteorological tower location.

Figure 5. Aerosol spectra obtained at locations 1 and 5 inneighborhood of SNI offshore breaker line. Dashedline is the difference between the spectra.

Figure 6. Calculated aerosol contribution to extinction forNOSC (x) and NPS (-) data as a function of time.Data was obtained during the NOSC-NPS intercomparison.

Figure 7. Relative counts per bin for CSASP-range 1 spectro-meter using 2.7 um diameter latex spheres.

Figure 8. Relative counts per bin for ASASP-range 1 spectro-meter using 2.05 um latex spheres.

Figure 9. Relative counts per bin for ASASP-range 0 spectro-meter using 1.1 um diameter latex spheres.

Figure 10. Relative counts per bin for ASASP-range 0 spectro-meter using 2.7 um diameter latex spheres.

Figure 11. Relative counts per bin for ASASP-range 0 spectro-meter using 2.05 um diameter latex spheres.

Figure 12. Relative counts per bin for ASASP-range 2 spectro-meter using 0.43 um diameter latex spheres.

4

Figure 13. Upper figure: plot of idealized spectrum showingassumed (solid vertical lines) and actual (dashedvertical lines) bin edges.

Lower figure: shift of dN/dr spectrum due towide bin.

Figure 14. Particle size calibration for NPS, 0, and Garmisch,0, spectrometers. The solid line shows correctsizing. The solid squares enclose the ambiguityzones for the spectrometers.

Figure 15. Extinction calculated from NPS aerosol measure-ments (solid line) and Calspan nephelometer(dashed line) as functions of time for 5/9. Theshaded blocks show times when the wind directionwas good.

Figure 16. Extinction calculated from NPS aerosol measure-ments (solid line) and Calspan nephelometer (dashedline) as functions of time for 5/10. The A's areNOSC aircraft measurements. The shaded areas showtimes when the wind direction was good.

Figure 17. Extinction calculated from NPS aerosol measure-ments (solid line) and Calspan nephelometer asfunctions of time for 5/15 on an expanded scale.The X's are values measured with a 6328 laser.The A's are NOSC aircraft measurements.

Figure 18. Extinction calculated from NPS aerosol measure-ments (solid line) and Calspan nephelometer (dashedline) as functions of time for 5/15. Trianglesare the Wells, et al. prediction.

Figure 19. Extinction calculated from NPS aerosol measure-ments compared to Wells' model, A, 6328 lasermeasurements, x, and 4880 laser measurements, 0.

Figure 20. Extinction calculated from NPS aerosol measure-ments compared to Wells' model

Figure 21. Comparison of PMTC measured optical extinction (0),extinction calculated from NPS aerosol measurements(x), and Wells' model (A). Results are presentedfor wavelength of 1.06, 3.75, and 10.59 pm.

Figure 22. log(dN/dr) vs log(r) for 5/15/78 - 1646. The solidline is the 7th order polynomial fit to the data.

Figure 23. log(dV/dr) vs log(r) for 5/15/78 - 1646. The solidline is the 7th order polynomial fit to the dN/drdata.

5

Figure 24: logt(dN/dr) vs log(r) for 5/15/58 - 2046. Thesolid line is the seventh order polynomial fit tothe data.

Figure 25a-25d: log(dV/dr) vs log(r) for 5/15/78 -2046. Thesolid line is the seventh order polynomial fit tothe data. The extrapolation methods used were:

a. polynomial extrapolationb. linear extrapolationc. constant extrapolationd. cut off

Figure 25a-26b: Log(dV/dr) vs log(r) for 5/8/78-0835. Thesolid line is the seventh order polynomial fitincluding polynomial extrapolation (a) and linearextrapolation (b).

Figure 27. Comparison of aerosol contribution to extinction asdetermined optically and from measured aerosol spectra.

6

I. Introduction

The capability to make accurate and reliable aerosol

measurements has been a major concern of the EO/MET program.

For the purposes of this program the word "accurate" means

accurate enough to predict the performance of optical systems.

Since the relative importance of the aerosol concentration varies

with the optical wavelength, the required accuracy depends on

particle size. Two methods are used to determine the usefulness

of a particular instrument: 1) comparison to other spectrometers,

and 2) comparison of optical parameters predicted from aerosol

measurements to those measured directly. One of the major efforts

undertaken in the FY79 EO/MET program has been to compare and

assess the aerosol spectrometers that are used in the various

experimental programs.

The Naval Postgraduate School (NPS) has performed a number

of experiments with two Particle Measurement Systems (PMS)

optical spectrometers over the past two years. The data obtained

can be used to determine the accuracy of these instruments and

how best to use this class of spectrometer in general. Program

spectrometer intercomparisons are being done by the EO/MET group

as a whole and therefore is not a subject of this report. The

purpose here is to present, in one document, the NPS measurementsand several results that should be useful to the EO/MET program.

Results from the following experiments are presented here:

1. CEWCOM-78, comparison of aerosol measurements with

Calspan visiometer, NPS ship to shore optics, NOSC

aircraft, and Wells' model.

7

2. CEWCOM-78, affect of offshore breaker line (-1/2 mi.)

on aerosol distribution at San Nicolas Island (SNI).

3. SNI spectrometer intercomparison

4. CTQ-79, comparison of aerosol measurements with NPS

13 mi. overwater optical range.

5. NOSC-NPS intercomparison at San Diego

6. Calibration and spectrometer intercomparison with

Max Planck Institute f!Wr Chemie, Mainz, F.R.G.

8

II. Equipment and Data Handling

NPS operates two aerosol spectometers: the PMS models ASASP

and CSASP. They are sensitive to aerosol particles with radii

from approximately 0.1 lim to 3 pm and 3 Um to 15 um radius,

respectively. The spectrometers operate in conjunction with a

DAS-32 data acquisition system. For almost all measurements the

slowest DAS mode is used, for which it collects data for 40 sec

then dumps, changes ranges, and resets. The data is collected for

30 minute periods then averaged by a Hewlett Packard 9825 computer.

Most of the experiments were performed aboard the NPS ship

R/V ACANIA. The spectrometers were mounted on a mast placed

approximately 15 feet aft of the tip of the bow so that the sampled

air was not conditioned by the ship. The mounting was 36 feet

above the deck, 43 feet above mean sea level. (Note that for the

CTQ cruise the mounting was 18 feet lower.) The spectrometers

air inlets are pointed directly toward the bow, with fixed orien-

tation requiring that, as a precautionary measure, we only accept

data when the relative wind is within 300 of the bow. Normal

operation is to head the ship into the wind during times of data

acquisition.

Both spectrometers have size regions where sizing uncertainty

exists, called ambiguity zones!1 )In these zones the optical sizing

cannot be expected to be reliable because the Mie scattering curve

is not monotonic. This leads to a situation where a given inten-

sity of scattered light corresponds to three particle sizes. In

Figure 1 we show the spectrometers responses vs particle radius

for 1.33 and 1.5 indices of refraction. (1) tones for which there is

9

ambiguity are shown as shaded, for both the ASASP, and CSASP spec-

trometers.

The full output of both spectrometers consists of 6

ranges, 15 points per range, for a total of 90 points. Due to

natural fluctuations, counting errors, ambiguity zones, etc. all

points are subject to uncertainties, even though one half hour

averaging is used. Because of the uncertainties associated with

individual points the correct manner to reduce the data is to

use some averaging technique, and we have chosen a fit using a

7th order polynomial for log(dn/dr) vs log(r). An odd order was

chosen because the data is odd in log space, and order 7 because

this essentially treats each range as a single point.

Some of the individual data points are discarded before

forming the polynomial fit. There are two reasons for excluding

data: 1) inherent inaccuracies in the small size bins for each

range and 2) the ambiguity zones. Figure 2 shows the bin con-

figurations of the various spectrometer ranges and the location

of the ambiguity zones. The shaded bins show regions of overlap

between the ranges.

We have used two schemes for handling the data, both of

which are compromises between eliminating ambiguity and rejecting

data from small size bins. The methods are:

1. Reject those small size bins which overlap with large

size bins from the next smaller size range. The bins

eliminated for each range are:

ASASP CSASP

3 2 1 0 Range 10

3 3 6 3 # of Bins Rejected 5 3

10

I IM

C)

C C

0

C4

(asudsokajouoilodS)Bo2Figure

CO

Ira

c0.0S .mcl0

rIg0 0

1 2

2. Reject smallest size bins and all of ASASP Range 0 to

eliminate its ambiguity zone. The bins eliminated

for each range are:

ASAP CSASP

3 2 1 0 Range 10

3 3 3 All # of Bins Rejected 1 1

Method 1 was originally used to evaluate SNI Intercomparison

data. Method 2 was developed using an independent data set from

the JASIN experiment. When method 2 was applied to the SNI data

the calculated extinction at the visible was increased by about

10% and no change resulted at 10.6 Pm. Method 2 was used to cal-

clulate the extinctions for the SNI Intercomparison report.

Figure 3 shows data points for a one half hour average period

plotted on a log(dN/dr) vs log(r) scale. The plot compares the

two methods. The solid dots are data points used in both methods,

the x's data points from ASASP range 0 which are not used for

method 2, and the open circles data points that overlap other bins

that are not used for method 1. The figure shows that method 2

eliminates the errors that can be introduced by the ASASP ambi-

guity zone in the 1 pm region, otherwise there is little difference

between the two methods.

One further note on the polynomial fit is in order. The

highest order polynomial term will always dominate the fit for

large argument. If the coefficient of the highest order term is

positive then the fit will ultimately go to large positive

log(dN/dr) for positive log(r) and vice-versa for negative log(r).

This turnover in the curve will cause erroneous results if it

occurs within the size range of interest (which often happens).

We prevent this from occurring within the size range

13

4-

r0

0

x ASASP-Range 43 0 Overlap Bins

3

og

2-2 0

xxxii xo

X 0

x 0 9~~0 x %

0- Xxx ..o

-1I .

00

-110

,log (rFigure e

i 14

used by generating two points outside the range of data, at

log(r) - +1.5, and adding them to the data. For -1.5 the point

is generated by using the average slope of the first five points

accepted in ASASP range 3. For +1.5 all points in the CSAP

range 0 are used to generate an average slope. The polynomial

fit uses all accepted data points and the two ficticious points.

Additional discussion on the effect of the added point at +1.5

will be found in a later section.

Extinction calculations are performed using the polynomial

fit, not the original data. The range defined by log(r) equal

-1.0 to +1.4 is divided into 48 bins, with ecual width of 0.05 in

log(r). The average dN/dr in each bin is calculated from the

polynomial then the contribution to the scattering is calculated

using the appropriate Mie coefficient.

15

III. San Nicolas Island Breaker Line

We present these results first since they impact directly

on ongoing programs. SNI is used for many EO/MET and Optical

Signature Programs (OSP) experiments. It was chosen partially

because the island is located approximately 90 miles from the

coast of California and could fairly closely represent open ocean

conditions. An optical range and tower for meteorological measure-

ments are located at the north end of the island which is the

location used for the SNI Intercomparison reported below.

Shoals are located approximately 1/2 N mile offshore, to

the W of the range (see Figure 4) and an exposed rock is located

8 N miles to the NW. We have been concerned that the frequent

breakers across the shoals could introduce a significant quantity

of sea spray droplets into the atmosphere and compromise shore-

line measurements.

During CEWCOM-78 the NPS ship R/V ACANIA operated in the

SNI area. The ship was equipped with a complete suite of meteoro-

logical equipment and the two spectometers. (2) One of the purposes

of the cruise was to test the respresentativeness of SNI to open

conditions. Results for small scale properties (e and CT 2) have

been reported previously. (3) The particular test reported here

was designed to assess the effects of the breaker line and not

the influence of the island itself. In order to determine the

influence of the island it is necessary to make measurements at

sea and on the island, preferably with the same instrument. Some

of the results presented later in this report could be used to

check for island influence on the aerosol spectrum but lack of

16

Jc0

Figure 4 ,

17

cross calibration between shore and ship instruments would

make the comparison of dubious value.

In Figure 4 we show the orientation of the island, the

location of the shoal and five positions at which the ship was

stationed for aerosol measurements. In Figure 5 we show aerosol

spectra obtained at positions 1 and 5, and the difference between

the spectra. The measurements were made when there was a light

wind (6 knts, 300*) approximately from the shoal toward the island.

The occurance of light winds was fortunate since local generation

from surface waves is then minimal and the breaker effect would

be easily observed. At position 1 there was a large increase in

the number of particles with sizes of 3 u and above relative to

position 5. These are the sizes expected for the local generation

contribution to the aerosol spectrum and are obviously generated

at the breaker line.

These results appear to be very serious with regard to the

representativeness of the island to open ocean conditions. Since

the prevailing wind is roughly in a quadrant about NW one can

expect the horizontal transport of aerosols generated at the

breakers to influence the aerosol spectrum at the island a sig-

nificant fraction of the time. We draw this conclusion from the

fact that, with the ship directly between the island meteorologi-

cal tower and the shoal, and the local wind at 3000, the ship

detected significant shoal influence. When the wind is more

westerly the effect should be worse. When the wind is more nor-

therly, the effect should disappear, but this is the wind

direction for which continental influence from Pt. Conception

18

i -- j

0 I I I

SNI5/18/78 1930-2100

* Position 1o Position 5-- Difference

-1-

"0

O2

1.19

0,

i -2-

~0

0

S1.0 3 10 30 100

Radius (1nm)? igure 5

19

will most likely occur. It is also possible that for a NW wind

the influence of Begg rock could be important. Obviously, no

definite conclusions can be made as to the seriousness of the

shoal and Begg rock influences without extensive testing.

These results also suggest another comparison that should

* be made: coincident aerosol measurements at the meteorological

tower and in the cove near the optical paths. The meteorological

tower at SNI is on the tip of the island and the optical range is

in a cove where local breakers could influence the optical measure-

ments.

20

IV. San Diego Intercomparison

As a preliminary to the San Nicolas Island Intercom-

parison NPS and Naval Ocean System Center (NOSC) performed an

intercommarison of their spectrometers at San Diego. The

spectometers were installed side by side on the roof of building

323 at NOSC and operated for four days, 1/22 to 1/25 1979. The

roof is approximately 30 ft high and the building is located on a

shoreline bluff approximately 100 ft above the sea surface.

The results of the intercomparison are shown in Figure 6.

The extinction was calculated from the measured aerosol spectra

by each laboratory for their respective data for a wavelength of

0.53 lim. (4) Figure 6 shows extinction plotted as a function of

time, with a solid line for NPS and X for NOSC. The results are

quite good. There is a systematic discrepancy of approximately

a factor of 2 during the morning of 1/25. This was a time when

high winds were experienced, the wind exceeding 20 knts from

0400 on. No explanation is offered as to why a high wind would

cause a systematic difference in measurements made by the two

types of spectrometers. For the remainder of the measurement

period there was no systematic error. A wide variety of wind

speeds and directions, except high winds, were experienced and

the spectrometers always operated satisfactorily.

21

-NPS XXx NOSC xXX

xX xxxx x

xx

0.1 XX x

Ex

xxx

0.01-

17 22" 12 24 12 24 12 (PDT)22 23 24 25

JAN 79

Figure 6

V. San Nicolas Island Intercomparison

During the first two weeks of May, 1979, several labora-

tories installed equipment at SNI to perform optical extinction

and aerosol measurements. The purpose of this intercomparison

was to try some new optical techniques and to determine the

validity of the aerosol spectrometer results. The NPS aerosol

results are too voluminous to be reproduced here. They are in

a special project report which is available to anyone interested.(5 )

Sample outputs of intercomparison data are presented in Figure 7

and Table 1. The table lists bin center radii, the measured

values of dn/dr and the 7th order polynomial coefficients, where

S7-ilog(dN/dr) = Z ai (log r)

i=O

The ' gure shows the data points plotted as log(dn/dr) vs log(r),

with the points alternating between + and 0 to delineate ranges.

The solid line is the polynomial fit.

The test of the aerosol spectometers is to be made in two

ways: 1) direct comparison of the spectra produced by the

various spectrometers, 2) comparison of spectrometer extinction

predictions and optically measured values. Comparisons will be

presented in a report on results for all instruments which is

being prepared by NOSC.

Table 2 lists the NPS determined extinctions as a function of

time which are to be used for the intercomparison.

23

.3J1 Intercomparisin 4 /30/79 1542

r and dJ/dr

0.096 4.82E 03 0.159 2.51 02 0.330 7.2.1 010.100 3.49E 03 0.171 1.93E 02 0.350 5.45E 010.104 2.55E 03 0.184 1.49E 02 0.370 4.65E 010.109 1.900 03 0.196 7.69E 01 0.390 4.01E 010.113 1.65C 03 0.209 5.71E 01 0.410 4.49E 010.118 1.45E 03 0.221 8.79E 01 0.430 3.539 010.123 1.08E 03 0.234 5.05E 01 0.450 1.92E 010.128 8.85C 02 0.246 9.01E 01 0.470 2.72E 010.133 8.24E 02 0.259 6.37E 01 0.490 1.28E 010.138 6.43F 02 0.271 1.08E 02 0.250 0.00E 000.143 5.82E 02 0.284 7.91E 01 0.000 0.00E 000.148 5.49E 02 0.296 6.59E 01 0.000 O.00E 00

0.580 1.55E 01 1.479 9.44E-01 3.685 8.71E-020.660 9.62E 00 1.671 1.16E 00 4.452 3.83E-020.740 7.03E 00 1.863 1.29E 00 5.219 2.32E-020.820 4.81E 00 2.055 1.05E 00 5.986 1.09E-020.900 2.96E 00 2.246 5.45E-01 6.753 1. 05E-020.980 2.40E 00 2.438 2.469-01 7.520 7.00.--031.060 5.55E-01 2.630 2.86E-01 8.287 6.77E-031.140 1.85E-01 2.822 3.OOE-01 9.054 4.51E-031.220 1.85E-01 3.013 2.71E-01 9.821 4.189-031.30U 1.85E-01 3.205 1.91E-01 10.588 1.92E-031.380 3. 70 -01 1.651 0.00e 00 11.355 2.14E-031.460 5.55E-01 0.000 0.OOE 00 12.122 2.03E-03

Order 7 Polynomial Fit

al 3.027E-01 a2 -2.855E 00 a3 4.983E-01a4 1.773C 00 a5 -7.277E-01 a6 -2.d04E 00a7 4.042E-01 a8 8.813E-UI

Table 1

24

4L

San Nicolas IslandNPS data

4 /30/79 1542

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27

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28

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32

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34

VI. Calibrations at Mainz and Garmisch

One member of the Environmental Physics Group (K. Davidson)

spent six months at the Max Planck Institute fur Chemie, Mainz,

F.R.G. performing detailed calibrations of the NPS spectometers.

The majority of the time was spent working with the group at

Mainz, shorter visits being made to Garmisch-Partenkirschen to

discuss spectrometer intercomparisons. Investigations were under-

taken on:

A. Particle sizing--ambiguity zone effects

B. False sizing due to bin edge shift

C. Particle density calibrations

D. Counting statistics

E. Spectrometer comparison

A. Particle sizing--ambiguity zone effects

Sizing of particles by the spectrometers was calibrated

using a generator developed by Jaenicke. (6) The generator produces

a monodisperse aerosol using latex particles, the particle size

being specified by their manufacturer. The results from several

of the calibrations are shown in Figure s-12. Special attention

in these measurements was paid to investigating the ambiguity

zone effect.

Figure 7 and 8 show results for the CSASP spectrometer,

range 1, using 2.7 and 2.05 pm spheres. The sizing was found

to be quite good, with the ambiguity zones having little effect.

Similarily good results are shown in Figure 9 for ASASP range 0

for 1.1 um particles.

Quite different results were obtained for the ASASP, range 0,

35

using larger spheres, 2.05 and 2.7 um. The results are shown

in Figures 10 and 11. The spectrometer placed these particles

in bins 3-7, which is 1-1.8 pm. The shift of these sizes to

lower bins cannot be accounted for by the ambiguity zones for

latex (n = 1.5). However, if the particles had an index of

refraction of 1.33 the shift to lower bins could be easily ex-

plained. It was noted that during several of the calibrations

the humidity was not well controlled, as evidenced by conden-

sation on the walls of the generator. This means that the latex

spheres could have been water coated, lowering their index of

refraction (n = 1.33 for water).

The final results presented, Figure 12, shows 0.43 pm

spheres sized by ASASP range 2. These results are somewhat

ambiguous. There appears to be a counting peak at bin 4, -0.32 u,

and a weaker peak at bin 7, -0.39 p. The spectrometer may have

sized incorrectly, or, one could interpret the results to be a

peak near the correct value false counts in the small size bins.

Finally, note that in all cases there are a large number

of false counts in the smallest size bins of each range. This is

probably due to the carrier material that is used to suspend the

latex spheres. Such effects have been observed at PMS.

B. Bin edge shift

The group at Garmisch has observed significant counting

differences between two supposedly identical spectrometers

operating side by side. They attribute the differences to

errors caused by bin edge shift when measureing very steep slope

spectra.

36

Ambiguity Zones

2.7Wm

120-CSAS P - Range 1

100-

.IO80-0

~60-

~40

20

0 -2.0 4.0 6.0 8.0

Diameter (14m)

Figure 7

37

Ambiguity Zones

180-

160-

140- 2.05 W m

~120O CSAS P - Range 1

0

~80

60-

40-

20-

0---0 2.0 4.0 6.0 8.0

Diameter (pm)Figure 8

38

Ambiguity Zones

120-

100- 1.pm

n80 ASASP - Range 0

460-

~40

20-

0 1.0 2.0 3.0Diameter (wm)

Figure 9

39

n 1.33

n 1. 5077774=

Ambiguity Zones

120- 2.7 pm

100- ASAS P - Range 0

0060-

0

20-

00 1.0 2.0 3.0Diameter (pm)

Figure 10

40

n =1.33

n =1.5

Ambiguity Zones

120 20 i

100-

w80- ASASP - Range 0

0

~40

H20 L

00 1.0 2.0 3.0Diameter (pjm)

Figure 11

41

30-

0.43 p

20-

0

ASASP - Range 2

10-

0-0.2 0.3 0.4 0.5 0.6

* Diameter (pm)

Figure 12

42

Figure 13 illustrates the effect. Two assumed bins are

shown by solid lines, and the actual bin edges shown with dashed

lines. With the edges shifted as shown, smaller sizes, with their

corresponding high numbers, will be sized into a larger size bin.

This will artificially raise the counts in that bin leading to

the spectrum shown by the dashed line in the lower figure.

C. Particle density calibrations

A fair amount of effort was expended on attempting to

calibrate the aerosol particle density measurements. We had a

nearly complete lack of success for a very simple reason: it is

extremely difficult to determine the air flow rate through the

optically active volume of the spectrometers, at least with the

equipment we have available.

Our experience showed that the method of introducing the

aerosol into the spectrometer is extremely critical. If an

absolute calibration is to be of any value the aerodynamic flow

must be matched to field conditions. In this regard, laboratory

calibrations should be made using the horn supplied by the manu-

facturer with air being drawn from a large volume using the

4 spectrometer fan.

Our limited experience with these laboratory calibrations

and with four long duration cruises have identified the following

as potential causes of counting errors:

1) The incidence angle of the wind can change the results.

This effect is wind speed dependent.2) Turbulence in the scattering chamber will affect the

43

AssumedBin Edges

TooActualBin

d (log r)

I I

d N

d (logr0

Assumed

r

Figure 13

44

calibration. This can occur during high wind situa-

tions.

Note that the above shows that a spectrometer designed for air-

craft use cannot be used on the ground unless it is aspirated

at a rate equal to aircraft speeds. It will not be sufficient

to correct for the wind speed difference in order to calculate

the total volume of air that has been sampled. (Needed elec-

tronics modifications for rejection, etc. are not addressed here.)

D. Sampling statistics

The Garmisch group probably has more continuous experience

with the PMS counters than any other. They view the sampling

statistics to be very important when describing distributions

which change by three orders of magnitudes over the size intervals

of interest. Obtaining reasonable statistics for the low con-

centrations at large sizes requires that sampling times at these

sizes must be much longer than at the smaller sizes. A second

consideration is that the total sampling time to cover all sizes

must not be too long. The present sampling is (for ASASP ranges

0, 1, 2, 3; where range 0 is for the largest particles) as follows:

Range

0 30 seconds

0 30 seconds

1 30 seconds

2 30 seconds

3 30 seconds

0 30 seconds

0 30 seconds, etc.

45

This sampling results in 40% of the sampling time being given

to the larger sizes. The opinion of the Garmisch group is

that the largest sizes should have at least 75% of the sampling

time in order to have optimal statistics. (It is important to

note that 20 to 30 minute total periods are the most one can

expect when the operation modes include other platforms or

measurements.) The Garmisch sampling is as follows for a 20

second total period.

Range

0 14 seconds

1 3 seconds

2 2 seconds

3 1 second

E. Spectrometer comparison

The Garmisch and the NPS spectrometers were calibrated

using the aerosol generator at Mainz. All results are shown on

a single graph in Figure 14. The results show that the NPS

spectrometers tended to size particles slightly too large. In

general the results are quite good. The figure shows the ambi-

guity zones and we see a definite scatter of the sizing in these

zones, as expected.

46

6.0- * NPS Spectrometers0 Garmish Spectrometer

4.0-

~2.0-

E.2 Ambiguity

00

z~0.6-

0.4-

K 0.2-

0.2 0.4 0.6 1.0 2.0 4.0 6.0Particle Diameter (pm)

Figure 14

47

VII. CEWCOM-78 COMPARISONS

There were opportunities to compare several instruments,

during CEWCOM 78: NPS spectrometers, Calspan nephelometer and

particle measuring equipment, NOSC airborn aerosol spectrometer,

NPS ship to shore lasers, and PMTC optics. The Calspan equip-

ment was on board for the full cruise, while the laser, aircraft

and optics measurements were made only at SNI.

The Calspan equipment on the ship was:

Height AboveInstrument Parameter Sea Surface

Thermo-Systems Electrical Aerosol size dist. 5.0 mAerosol Analyzer Mod. 3030 (0.01 - 75 im)

Royco Model 225 Particle Aerosol size dist. 5.0 mCounter (0.3 - 5 im)

Calspan Sea Spray Sampler Aqueous aerosol spectra 3.Om(gelatin repl.) (3 - 100 urm)

Gardner Small Particle Total aerosol conc. 5.OmDetector (>0.0025 iim)

Thermo-Sys. Electrostatic Aerosol chemistry by size 5.0 mAerosol Sampler, Mod. 3100 (>0.02 pm)

Hi-Vol and Lo-Vol Filter Bulk aerosol chemistry 5.0 mSamplers (2)

Calspan Fog Droplet Sampler Fog drop size dist. 3.0 m* (gelatin repl.)

EG&G Forward Scatter Meter, Visibility (60-6000 m) 7.5 mMod. 107

MRI Integrating Nephelometer, Scattering Coeff. (0.1 - 5.0 mModel 2050 100x0-4 m-l)

Visibility (5-80 km)

We list the full compliment of equipment for completeness only.Comparisons have not been made to all of their results.

The NOSC aircraft carried a PMS ASSP-100 spectometer. NPS

48

optical measurements were made ship to shore using 4880 and0

6328 A wavelength lasers, and an IR broadband source with

3.6-4.0 im and 9.0-12.0 l.m detection filters.

A. Ship and Wind influence

The effect of the ship and wind direction on the measure-

ments are most easily seen by comparing the NPS spectrometers

to the Calspan nephelometer. (8)These results are shown in Figs 15-

18, where the spectrometer (solid line) calculated extinction

and nephelometer (dashed line) measured extinction results are

plotted as functions of time. The measured extinction is for

visible and the calculated is for 0.488 um.

Figs 15 and 16 show the wind direction effect. The shaded

bands in the figures show times of "good" wind direction, where

good means within 300 of the bow. We see that with a good wind

direction the spectrometer results show a marked increase rela-

tive to the nephelometer. This feature was consistent through-

out the cruise. Turbulence in the spectometer sample chamber and

particle loss due to non-isokinetic sampling could be responsible

for the effect. Turbulence could cause reduced flow through

the scattering volume even though the average flow is correct.

With a good wind direction the air flow will be less distorted.

Ship influence and/or system location also played an

important part in the Calspan nephelometer measurements. All

figures other than 15 and 16 are for good wind directions.

Results in Figs 15-19 show that with good winds the nephelo-

meter gives much lower scattering values than the spectrometers.

This is apparently due to the location of the nephelometer

49

0~ -0

LU

0 -00

00I C~4e

I4 0

0-co 09- I 0

ODI 0

o(0 I 09- I 0

0*09- 9 0

(LUWtOL)

Figure 15

50

CEWCOM -785/10/ 78A

2.- A- NOSC Aircraft A

0

~1.0

0.5-/

0000 0800 1600 2400Time

Figure 16

51

/ 0/0

000

0 0

-- 0

4ym4

LOLUV-L)7Figur 17

G~US0

sampling tube on the ship and the influence of the long inlettb(9)

tube. (This effect is especially apparent later in the day on

5/15. During that time the wind was continually increasing

(reaching 60 knts at times) and the Acania continued operation

until the anchor chain broke. The spectometers were in an

elevated and exposed location and registered a very large increase

in aerosol density whereas the protected nephelometer showed no

effect.

B. Comparison with NOSC Aircraft

NOSC aircraft measurements are shown in Figs 16 and 17,

where they are labeled with an A. The results are summarized

below:

-4 -l1S(10-4m -

Date/Time NPS NOSC

5/15 0700 - 0900 1.4 1.6

5/10 1600 - 1800 1.5 1.9

5/12 1400 1.4 0.9

5/12 1600 1.4 0.9 (at 100 ft)

C. Comparison with NPS Optics

NPS optically measured extinction for 0.488 Pm and 0.6328 Pm

appear in Figs 17 and 19, with an X for 0.6328 and an 0 for 0.4880.

The measurements were made along an approximately 2 km optical

path from the RV/Acania to the shore on SNI. In Fig. 19 three

or more measurements were made very close together in time and

the average and extrema are plotted as a point and error bars.

All optically measured values h4ve had 0.2 x 10-4m - subtracted

53

from the measurement to correct for molecular absorption. This

is an adequate approximation to enable comparisons to be made

with the aerosol measurements.

There is fairly good agreement between the spectrometer

and optical results for all but one point. Further discussion

of the optical results is given in other reports. (10 ) No attempt

will be made to use these results to assess aerosol spectrometer

performance.

D. Comparison with Wells, Katz, Munn Model.

Figs 18-20 include extinctions calculated from the Well's

et al model ( ) , shown as A- We have used the model as modified

by Katz, taking the visibility correction term equal to 1, and

(12)using the Fitzgerald humidity growth factor. These comparisons

of the model and the spectrometer results are made only for times

when the wind direction was good.

The model performance was characterized by periods of

systematic disagreement and fortuitous agreement in specific

instances with the spectrometer measurements. In general the

model tended to underestimate the extinction. We will not

attempt to discuss model performance here, that will be the

subject of a later report. Here we merely present some easily

observed points from the CEWCOM-78 data.

1. For wind speeds above 10 m/sec (5/15) the model works

fairly well.

2. For low wind speeds the model underestimates the

extinction for most cases.

3. For the open ocean conditions of 5/20 and 5/10 (not

shown) the model overestimates the extinction.

54

4. The measurements do noL show a sudden increase in

extinction for wind speeds greater than 7 m/sec as

predicted by the model (5/19, 5/14).

5. The Wells' humidity growth term fits these data bette.-

than the Fitzgerald-Ruskin term.

All of these results are for moderate to high wind speeds.

For high winds the hydrostatic stability is near neutral. We

have found that stability plays an important role in establish-

ing the equilibrium aerosol distribution. We expect to find

less agreement with the model for non-neutral stability. This

topic is the subject of a report which is in preparation.

E. Comparison with PMTC optics.

During one of the days the RV/Acania was at SNI optical

measurements were made by PMTC. Approximately 6 hours of inter-

comparison data were obtained. The results are shown in

Figure 21 for wavelengths of 1.06, 3.75, and 10.59 lim. Wells'

model predictions are included for comparison purposes. The

optical data was supplied by Mathews of PMTC(13) Molecular

extinction was subtracted from the optical results using

LOWTRAN-III, the calculations being performed by NPS.

The agreement between aerosol and optical results is

fairly good, especially in view of the optical measurements

being made on the shore and the aerosol measurements on the ship.

5/15 was the day when very high winds occured late in the day

and the data show a systematic disagreement with high wind

speeds, the aerosol results being higher. No conclusive expla-

nation of this effect can be given; acceleration of the airflow

55

by the land could cause some large particle drop out, resulting

in lower extinction being measured near the island.

56

IL

CEWCOM -786.0- 5/15/ 78

-Well s Model

E24.0-

fwe

2.0-A

N/

01A

01 igr ISI

57

CEWCOM- 785/14/78

-Wells Model6.0- x - 6328 Laser

o - 4880 Laser

4.0- U,<71u>

2.0-

AA

0000 0800 Tie 1600 2400

Figure 19

58

00

N

1

oo'I

EE

00

Go 44

0)L tpcok r-

Figure 0

590

x0§

coofw _z j 0

L0O

10 I t

x 0\

00

E

00

0_

0~ 0I -0

Cl) Cl to0

V m cr) C4 C( TWrl1)

Figure 2160

VIII. Extrapolation to Large Sizes

Other workers have pointed out that large size droplets

contribute significantly to optical extinction for all wave-

lengths. (14) This is true even when the number density for large

sizes is many orders of magnitude smaller than for small sizes.

We have investigated this effect for NPS data with particular

emphasis on the following:

1. 7th order polynomial fit.

2. Artificial end points to force good behavior of the

polynomial fit.

3. Proper extrapolation beyond measurement range.

The best presentation of the data to illustrate the problem

is a volume plot. Figures 22 and 23 are plots of log(dN/dr)

and log(dV/dr), respectively, vs. log(r) for 1646 on 5/15/78.

Both presentations use the same dN/dr polynomial coefficients to

fit the data. The polynomial was generated from the raw data

plus the artificial end points using method 2. The log(dN/dr)

plot looks quite reasonable, showing a monotonically decreasing

function that fits the data quite well. The log(dV/dr) plot

shows that the end point and the manner in which it is fitted by

the polynominal are significant for extinction calculations

since dV/dr is highest near the end point.

Table 3a lists the fractional contribution to the extinction

for various size ranges. This is done for 9 wavelengths from

0.488 to 10.59 pm. The data used is the same as that for Figures 22

and 23. The contribution shown for a particular size is the total

61

contribution for all sizes in a bin with upper radius the stated

size and lower radius the previous size listed. For 10.6 um

wavelength one expects the larger sizes will be the major con-

tributor and this is what is observed. For 0.488 pm wavelength

the large sizes (sizes greater than 8 pm) contribute 30% of the

calculated extinction.

The volume plots can be used to obtain an immediate estimate

of the relative contribution of the various sizes to the extinc-

tion. Ignoring the Mie coefficient the scattering is proportional

to

tfdN/dr)A (r) dr

where A(r) is the particle cross sectional area. Taking volume

V a A(r)r and dr/r = d(log r), the scattering is proportional to

,fdV/dr)d(log r)

Thus, a constant log(dV/dr) vs log(r) plot shows a roughly con-

stant contribution to scattering with size. Of course a Mie

coefficients must be used in an extinction calculation and it

does not become appreciable until the particle radius is about

one half the wavelength. Thus, smaller sizes do not contribute to

the extinction regardless of the magnitude of dV/dr. The data

from 2046 on 5/15 has a larger number of particles in the large

size ranges and is useful for examining the effects of extra-

polation. We have used 4 extrapolation methods to obtain

extinction values for this data:

1. Polynomial: This is the standard NPS technique where

the 7th order polynomial fits al the data plus the

62

2'nc - ,) File :lJ2

a'te 3/15/73 L'.e i' :I S

Averaiinq ti~e = ZC MnnutaS1:(d'./3r)- 5 ?olvrorrial of crier 7I 7.63,o116E-cJ2

-. 3522723E-61

i 2.1 .323>4E U)I~ 5 5 0I. ;5) - 0 1,

-2. 7517 ,) C0b.367430D[- 1

00

* * Polynomial**1 Extrapolation

ioi riliis-----------------------------------------

ia 1 e .]t nctio-1,a~ legt tinctionl1

J.4330 1.3172-Cl - -i0.53d0 1.516 F'- 01J. 323 1.5172-01 'J.3400 1.49JC-011.0330 1.541-011.0000 1.4907-011.3000 1.4 21E-C1 - -2 03.7500 1.159E-01

10.5)00 3.324F-02

-- 3

-- 4

Figure 22

63

face i U File 14102D ate 5/15/78 -rir'e 16 :4 b

Averaging tine = 20 -ninuteslog (dV/dr)- P olynor'ial of order 7

7.0'2u6l09C-O2-0.6532722E-01-1.00C9504t:-012.1382224E 00

-2. 1556934E-01-4 -1.5309714E 00

2.48.20 201 .-011.30b6316E2 00

-3

.Lo4 radiuz--- -------------------------------- I--- -------------------

).33j) i .) .- Gld.3. .317L:-C1 Polynomial

J.300 .4tO Extrapolation1.>0' 1.4 10r-01

1 .ko0 1 .4 21 0 -1 - 23.7500 1 .13,j-6110.5jl .$3OC0

-- 3

--4

Figure 2364

--'. _ .ID C; -* D C - - n r

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C CC C CC CC CC C C Z. a) C c '

N -r n Z DN A 'r A ' C 1

65

"?are * J File 4107Date 5/13/73 ri.-e ::46

Averag3ing ti',e = 20 -,iinuteslcI:(j"/dr) 5 2olvnoial ct orJer 7

1.1303745E-Cl-4 . 4 6 I6 C-0 1-3.213547-E3C11.5956871L 06J.463777£-0 1

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1

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-i --- - -

-i

,avelenitn Extinction0.4380 4 .321E-G1 - -I0.53J0 4 .313E-01 o0.5323 4 .3j30E-O0 c0.8400 4 .336E-01 c1.0300 4 .661E-011.0630 4 .36GE-01 0

1.6000 4.259E-01 - -23.7500 3 .857E-01 o

10.5900 3.530E-01

-- 3

-- 4

Figure 24

66

j ;- V 3/15/78 Tir:e 20:46

Averaqin] i e 20 tjinuteser 7Loci 3 r 5 polvnomiel cf order 7

I.IS03744C-01-4.4606105=-01r~-5.2135474-E-011.595887CE 008 .4 63 776,1I£-0 I

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0.53301 4 .313C-CI0.6323 4.3 3JFI- Polynomial0.84 00 4.336-01 Extrapolation1.03JO 4 .6 61C-011.0o00 4 .3 36 L- 011.O600 .2)F-0 - -2

3.7 5:)0 3 .85 7 E- 01

10.59,3C 3.53 E-01

-- 3

-- 4

Figure 25a

67

- D 'm CD a - a 0 4 aN a~ -V " a r* a ) a% a 4 -. a

. .a 6 . a 0 a . . . . . .

o -) o 0000000000000000000000 I M" i W" I

0aCD 0 0 DD 0 0 0 0 0 000 00 000 0000 0 0D

.=O a C a DD ) :DO O5 aC . . .

.4. c; c; c --l C;00 8 80 1 008

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0~ D a 0 aD aD a) aD a a 0 aD a a' a D a a a a CD a D r-4

4J 0ot

~ 0.4. -W _, )0 - D0 u RT- nL sI O .

c 00) 00 DC 0 0 0 0 00 c0 0 0I0 CD00000 0 -

C0 0 C000 03C CDa 0 00000 C DC 0000000 0 C;:

as 4 C1 aI a- - a a" a a1 %D a ao a a In fn aN a In a m a fn -W ar 0 a NMMI " NI I N(4I Nr nw R

LI ( -4C I C C C ' C C I :C -~ .

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face 4 0 File #107,),te 5/15/78 Time 20:46

Averacinq tie ne 20 ninutes1o 4(5V/r) Polvnomial of or,er 7

1.1303744 1 -01-4.4606105S-01-5.2135474"-011.5953870E 008.4637768"-01

4 -1.5030252E 001.013422'E-01

1.5442277E 00

- 3

0 CO

log radius------------------------------------ I-- -------------------

-1 1 2

t'aveleijtn Cxtinction0.4330 3.579E-01 - -L0.5300 3 .570E-010.u323 3.530E-010.8400 3.592z-01 Linear1.0330 3.812E-01 Extrapolation1.0500 3 .622E-011.6000 3.443E-01 - -23.7503 3 .090E-01

10.5903 2.630E-01

-4

Figure 25b69

a C C 0000D0C) c 0 Q 000 a;

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0 a 0 Ck * 0 CD * CD C . * CD a CD 0 C) I-)

00 0 00 0 0 00 0 000 0 000 ' . kMt 'NC)M r"Dr 4

-- a= a 0 0 a .4 M U) ao in *r al M (n .1 aN *' m . t a

0

0

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an 000 o 4 n m ent o nm( Nr , - ^

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(%4

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70

r ane 4 0 File "'107D ate 5/15/78 Time 20:46

Avera-4in-7 ti:,.e =20 -iinuteslo5,I/r Polyn~omial oil orc3er7

1.1303744L-01

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-3

2

loi r3diusI-------------------- ------------------- -------------------

0 .4 88 D3 3.046E-01 --

0.53,00 3 .034;:-0]0.5323 3.04OC-01 Constant0.3400 3.05?E-01Exrplto1.0300 3 .15 C-01Exrplto

1.0300 3 .077E-011.600J 2.)54E-01 - 23.750'3 2.538E-0)l

10.5900 2.l-l

-- 3

--4

Figure 25c

71

:M " 000D0a000Z0000 -00-I N - OQ -T-W -4-N0~ ~ ~ ~~ -:Z . . . .

* .a * * . .* . . . . . . . . . . .00 0= a00 0 0 C3 00000000 00 C.000

* 00 C 0 0 0a 0 0 CD 0 0 0 0M a 0 0m 0

0

4.J

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41 0

a = = v 0 a 4 0 C .= a . 0

UU

0n 0 M D en %D CN -a, N CS aw M Ia r an M an mr -12. r D 61

0 a a 0 0 0 10 :D a Ca 0 a a a a CD a) C -,. a C O= * *r

00 C - C C 80=; 1 000 a;0O Z0 IZ00 4z

I ul720

Tar~o i J File 107

A v r inq t ime =2c -inutesLc;(jV/Jr)- P,~ c~vrorria. cz orier 7

.iaJ3744,- -o-4.'46Col05L-01'-5.2l354l 4 L'-011.395367u.: GO3. 46377,'jLI-'JI

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-3

loi ra'Jijs--- --- -- --- -- - - --- -- --- -- --- -----------------------

-1

avalenjtn 6xtiflctiofl

0.4330 2.5224E-O1

0 .5323 2.556E-010.3430 2.526E-01Ctlf1.3300 2 .5 3 6L-1 Cu of1.0630 2 .541E-01I . )0 00 2 .417 E-0l 1 -23.7500 2 .008E-Ul

1U.5)00 I .440E-01

--3

--4

Figure 25d

73

-ZCNr. C00 0 0N-4 N -iv 0 =

*~~~C 0000000 0000 "N en 'z o

0 o m r- tn a% .j en . . at r% . aN N 7t a * .Z -4 r4000000r00W0000000000N0M0 0 0

0 0 0 0 ' D0C 0 4

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000 000 00 000000000 000)C

00 0 - N0 C40 rzqc C> 0 v= 1MNrnNMN 0 000 0 0 0 00 -4N -ON00 00 n T 0 T I00 I %-niD 0

C.1 0 00 00(4 ~ 0 0 c C 0 ;1 a m~ c C 0001

0 0

.4 00 0 0 0 0000 0 0 0 0

$4-

0

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a a a a a a a a a a a a aC00000000000000 0000- N Mar r 1 0 0.nW0000CDC

0 0 4N wrtn n wrtm 0 Ln-Kr-7 r tnfn II U %.0 0 C

40 00 0 0 0 00000000000 -. f) 0-

(a 74

created end point.

2. Linear: The polynomial is cut off at the middle of

the last range and the remainder of the fit is given

by a linear extrapolation from the cutoff point to the

created end point.

3. Constant: The polynomial is cut off at the radius of

the last data point (12 um) and log(dV/dr) is assumed

constant out to log(r) = 1.4.

4. Cutoff: The extinction calculation is cut off at the

radius of the last data point.

A plot of log(dN/dr) for these data is shown in Figure 24.

The 7th order fit looks very good and even the extrapolation

region shows no apparent problems. On the other hand the volume

plots show that the extrapolation technique has serious conse-

quences. The volume plots for these techniques are presented in

Figures25 and the corresponding extinction calculation results are

listed in Tables3. The results are summarized below:

PercentExtrapolation 0.488 m -1

Technique Contribution Extinction (km

Polynomial (25a) 41% 0'.432

Linear (25b) 34% 0.358

Constant (25c) 23% 0.305

Cutoff (25d) 0 0.252

Table 4

Shown are calculated aerosol contribution to the optical extinction

at .4880 um. The percent contribution due to extrapolated sizes

for the various extrapolation techniques is also shown.

75

The actual aerosol contribution to the optical extinction

should lie somewhere within the range given in Table 4. (Recall,

however, that all values are computed using a 25 pm particle

radius cutoff.) There is no unambiguous way to choose one of

the methods, but certain guidelines do clarify the situation:

1. The cutoff method assumes that there are no particles

with sizes larger than 12 um, which is unrealistic.

2. The polynomial method can give an unrealistically

high estimate of large particle sizes concentration

for some circumstances.

3. The linear and constant methods will give results which

are nearly the same for cases where dV/dr is nearly

constant but the results will diverge when dV/dr is

not constant.

We reject the cutoff and polynomial methods. The linear

method could overestimate extinction when the number of large

size particles is large (such as in a fog) and the constant method

will lead to overestimation for relatively clear air. Whichever

technique is chosen will lead to errors for some circumstances,

and this must be accepted. The best overall compromise is as

follows: Use the linear method for all cases where the slope of

log(dV/dr) vs log(r) is less than or equal to zero. For positive

slope the constant method is used.

The combination method will be used for future reduction of

NPS data, but has not been used in the past. Almost all past

data has been obtained during fairly clear conditions for which

the large size particles have a small overall effect. For such

76

conditions the polynomial method, which was used, is expected to

give good results. This is born out by the close agreement

between NPS calculations and optical measurements. Data which

was obtained during low visibility will be reprocessed. An

example of the type of data normally obtained is shown in Figures

26 and Tables 3f and 3g for a period during 5/8 -0835. log(dV/dr)

generally decreases with particle size and the large size con-

bribution to the 0.488 -m extinction is small. The polynomial

extrapolation looks terrible while the linear looks good. The

0.488 .im extinctions and % contribution from extrapolated sizes

are:

polynomial 0.064 km 7%

linear 0.058 km- 0.4%

The 7% contribution from the polynomial extrapolation could

produce an error of that magnitude, but that is acceptable. The

difference in the large size extrapolation does change the cal-

culated extinction at longer wavelengths appreciably. At 10.59 Im

-1the polynomial extrapolation gives 0.016 km and the linear

0.008 km- with 35% and 4% contribution due to extrapolated sizes,

respectively. Again this is not serious since for this high

visibility the molecular extinction is dominant at longer wave-

lengths.

77

taoe 4 0 File 4100Cate 5/ 8/7 Time 08:35

Averaginq tire = 20 minutesIocb(14/dr) 5 eolynomial of orier 7

-1.12¢4636£ Qo-6. 59U4644E-014.3230320E 001.5321367E 00

-5.3 2d15J6E 00S4 -1.7717637E 00

1.4477180£t 031.0340203 00

0

Ic'1 ralius * o0

I -------------------------------------I-- --------------------1 I.-i

, a velength Extinztion0.463J 6.449E-02 - -10.5300 6.273C-02C .u3 2 6 .0 23k-02 Polynomial0.3400 5.764E-02 Potyno li on1.0300 5.8d22-0. Extrapolationl.J600 5.7770-021.6000 5.696E-02 - -2

3.750 4 .4 13" -02I3.54u0 1.600E-02

-- 3

Figure 26a

78

'I N 4-4- 4 - N -T - * 0C 4j r- n - X ,D,

ur) 0 0 0: .-4 Ne r- M% CN X n LO -. ' r - ON CN -e in (N to

0 0 03 0 0 000 000 00 000 000 0o 00D 0nr 4- 1 4r

0) a DCDC

oJC -. 1 1 o I o '

00en e Ut 0mN 0r -L - IMr nr Nr

-H 0 ) 00 0 C) C a00 0 C 3 0 C) 0-4-4..m4CD ('CD,-4

4 J1xxC-4 C) -4- - rr 1I 7 - O-T N - 4C ,

-40U

n 000m00t0- m -n000c00a4

0

tn C, C'~( ~4~.5~ 4~ %3 O~( i- 4 N Y' N -4

0DC C 0 00 0000 00 00 0 0 000 000 0- 0D

CD a 0 0 0 C ) 000 000 0l 0C 0 0 00 00'44

1 1-4

-4 -4 -4 -4 rN

79

i ~ ~ Uae File #100

Cate 5/ 8/78 rile 0835

Averaging time 2U minuteslog(dV/ir) 5 Polynomial of order 7

-1.1204S36E 00-8.39U04o94 E-Ui4.52303206 002.5321367E 00

-5.5281586E 00- -1.7717637E 00

1.4417180E 001.0340203E 00

-3

-2

0 *

* 001

1og radiis *0-i 2-------------------------------------- ----------------

-1 1 2

.a ve1engti Extinction0.4880 5.814E-02 - -10.530C 5.636E-020.G32d 5.3826-020.6400 5.1275-021.0300 5.213S-J21.0600 5.117E-02 Linear1.6006 5.245r-02 - -2 Extrapolation3.75C0 3.750Z-02

10.5900 7.)09E-03

-- 3

-- 4

Figure 26b

80

) 0 C.000 ( L 00000--- 0 P00 N 0 C-50mV0

CN-4- 0000D0C0000000CD00=000

0 0 a = 00 = 0 4(1 m-M -m- ne - 41O 00OO0110

00 0 00 0 00 00C )000- 40 0000-)0 0 0 0 0 0 C

0

0 0000000 4 rr-(1 -4 0 00000000000D C 0000

0

0 ~ 0 000 -J n NC D -4 W ^I r" 4= M C 0.140 00 0 0 00 0 0 04 j S S S S S S

oz 0D 0 00 C:-f-I-- -4-1C m

U 000 0 0- - -4 0 0 0 0 0

0J m m a .D . -'. . * D00 0c

4.) 4-I

000 C; .J; , -; ; -4 ; 000000 ;

'-4

-, M

ff - o- Mr -p% TC -- C4L -D - -- n( 4-

Lfn

.~. ~O300C') 1 '4.-.-40 000

0Dt, 0000 0 00 000 4 40 CD 000 M00 0

c; C ; 1 C 1 c; ; C CS ,

81

IX. CTQ-79 Comparison with NPS Optics

In June of 1979 NPS conducted a research cruise on

Monterey Bay. The purpose of the operation was to determine the

proper scaling expressions for overwater water vapor transport to

be used in optical propagation models. 16 ) Coincident overwater

optical measurments were made in order to compare measured and

calculated extinction and scintillation. Since the ship was not

dedicated to optical comparisons, these data were obtained as

targets of opportunity and the number of comparisons is not large.

The Knollenberg ASASP and CSASP spectrometers were mounted

on the access platform of the RV/ACANIA meteorological mast at a

height of approximately 10 m above mean sea level. This is higher

than the average height of the optical path. Optical measurements

were made on the NPS 13.6 km optical range which has end points at

Pt. Pinos and Marina. Both end points are immediately adjacent to

the shoreiine.

Optical extinction was measured at 0.4880, 0.6328, 0.84, 1.03,

1.06, and 11.05 pm. The molecular contribution to the extinction

was computed using LOWTRAN III B (17)adapted for use on a Hewlett

Packard 9835 computer. Meteorological input data for the calculation

was obtained on board the ship. Subtracting the calculated molecular

component from the optically measured extinction yielded the aerosol

extinction. The wavelengths used for the comparison were chosen

because the optical filters used are narrow which simplifies the

LOWTRAN calculation. Rather than integrate over the width of the

filter, it was possible to simply calculate the molecular component

82

for a 5 cm-1 wide region at the center of the filter band. This

was the method used for the results presented here.

The aerosol contribution to the extinction was also calculated

from the measured aerosol spectra by the methods outlined earlier

in this report. Due to the method of obtaining the data, it was not

possible to use the new binning method, but the combined linear-

constant extrapolation to larger sizes was used.

The results are presented in Table 4. The extinction in units

of 10- 2 km as measured optically, the calculated molecular contri-

bution, their difference, and the values calculated from the aerosol

spectra are shown. A comparison of the aerosol extinctions as

determined from the two methods is also shown in Figure 27. The

figure shows that the aerosol spectra determined values are higher

than optical for all wavelengths except 11 pm. (The optically

measured values for 0.4880 pm appear to be in error.) The systematic

error is approximately 40% comparing to the optical value. The

comparison is expected to be poorest for long wavelengths where

the molecular extinction is dominant since the difference between

two large numbers is expected to yield large errors. However, this

is not true for these data. The percent error at 11 pm is not

significantly different and, in addition, the systematic difference

is not present.

It is not possible to identify the source of the systematic

difference. Five sources are possible: (1) aerosol measurements,

(2) optical measurements, (3) LOWTRAN calculation, (4) aerosol

calculation, (5) path average different from point measurement. The

extrapolation method of the aerosol calculation is suspect but the

83

(n OH- C14 D 00 r, 0-

10 .0 0. .n .n0 nc 40 mM9N- i N- , a% DwL L nL n

m n( nV0 nL )- n nm NC4( 1 4NNC

U4 Lnr

0 4L - N0MC4 4w 4vLo4N nL ou)wo wON0 -- jr c 4m% oa%% o

00 4. 0"rHO ~O-4 IN 'C)~ mV ~ ~ ~ H N HH-

4H

-4 rI N. r~H-LfNr- -4qw N H.4f vH nmm qc o0n( n nc r4c r-4 P- n -4 4

r-.j E-o -

(M rH -W en~ w en %O en "T ON HO C% -W mO 00 as f 0 rIn 0 % Oh m~ V ' %D

coo Lo~no-oC -oLno0 0 0 cfn "-. N ............ . ..Oza. .c. cOC4 ac

&0I HH4 P OOOHHHHHHHHOOHHHHHOOHHOOP-HHr-4O"-I

LAA~ 00%DO00

N.- 11% 00

2-' HH H H HHHHH4

-r-4

40

fn1 0N O rr. en 0 e

cc a~. 00.-0 .00.

r. 0 cOn OflN )ch 0N'Jt

E-4 N4 a o-4

41 00 00

~ .~0 3 )Ll: 85

0(

0 40

0 0 _00 eI

-

_I C 0 o xN0OD 00 lr Dc

0' 0

(00 EV

1C

Figure 2786

long wavelength results are most sensitive to the extrapolation

and it is here that the comparison is best. Apparently, the

extrapolation technique works reasonably well. Even with the

systematic difference these results are quite good since a 40% error

is within acceptable bounds for EO/MET applications.

LOWTRAN note: The LOWTRAN III B and LOWTRAN IV codes were

found to have an error which produces erroneous results for 1.06 rm.

This is due to peculiarities in the division of the wavelength spectrum

into bands. For details, contact NPS.

87

X. Summary and Recommendations

The PMS spectrometers owned and operated by NPS have been

calibrated and operated under a wide range of conditions. Com-

parisons have been made with other aerosol spectrometers and

with optical equipment. No systematic instrument errors were

observed that couldn't be accounted for by external conditions,

or by the ambiguity zones.

In general the units performed quite well, but certain

problem areas exist, which are listed below:

1. For wind directions greater than 300 away from the

inlet the number of counts decreases.

2. At high wind speeds it appears that the air flow rate

in the scattering chamber increases, thereby increasing

the apparent particle density.

3. Noise counts are registered in the small size bins of

each range and the magnitude of this effect depends on

system cleanliness(15)

4. The percentage of the counting time for large sizes is

too small, giving poor statistics.

5. Ambiguity zones cause incorrect sizing within some

ranges.

These problems do not make the spectrometers ineffective

but mean that they must be used with care. We recommend the

following:

1. Provisions must be made for keeping the spectrometer

pointed into the wind.

2. Delete at least the first 3 size lines from each range

for the ASASP.

88

3. Fit all data with a low order polynominal in order to

smooth over ambiguity zone errors and expected data

fluctuations.

4. Don't use a spectrometer for a purpose for which it

was not designed (interchanging aircraft/ground based

units) without insuring correct mean and turbulent

flow through the sample chamber.

Changing the counting time fraction would require a factory

modification and is not an option available to the operator.

Laboratory measurements should be made to determine the

sampling chamber flow rate under various wind conditions, par-

ticularly high winds. This would enable corrections to be made

to the data for high wind conditions.

Note that method 2 used for NPS data is essentially the

same as that used by Trusty of NRL. He replaces all data for

range 0 of the ASASP with a single point.

Note that there is an error in the LOWTRAN code as described

in section IX.

Finally, in our opinion, the types of spectrometers used

by NPS perform sufficiently well to be used to determine the

aerosol contribution to optical extinction for EO/MET applications.

89

References

1. Pinnick, R. G. and H. J. Auvermann, J. Aerosol Science10, 55 (1979).

2. "Experimental Aspects of a Shipboard System Used inInvestigations of Overwater Turbulence and ProfileRelationships," T. M. Houlihan, K. L. Davidson, C. W. Fairall,and G. E. Shacher, NPS-61-78-001.

3. "Atmosphere Marine Boundary Layer Measurements in the Vicinityof San Nicolas Island during CEWCOM-78," G. W. Fairall,G. E. Schacher, K. L. Davidson, and T. M. Houlihan, NPS 61-78-007.

4. Results calculated and made available by D. Jensen, NOSC.

5. "Results of Naval Postgraduate School Aerosol Measurementsfor San Nicolas Island Spectrometer Intercomparison,"G. E. Schacher, C. W. Fairall, and K. L. Davidson, NPS 61-79-011 PR.

6. Jaenicke, R. J. Aerosol Science 3, 95 (1972).

7. R. Knollenberg, private communication.

8. "Reduced Data from Calspan's Participation in the CEWCOM-78Field Experiment of the Coast of Southern California duringMay 1978," E. J. Mack and T. A. Niziol, Calspan Report #6232-M-2.

9. Gene Mack, Calspan Corporation, private communication.

10. "Optical Experiments in the Marine Boundary Layer," E. C.Crittenden, A. Cooper, E. Milne, W. Rodeback, R. Armstead andS. Kalmbach, NPS 61-78-006.

11. Wells, W. C. and M. W. Munn, Applied Optics 16, 654 (1977)

12. "On the Growth of Aerosol Particles with Relative Humidity,"J. W. Fitzgerald, NRL Memorandum Report 3847, 1978

13. G. Mathews, unpublished data, Pacific Missile Test Center.

14. G. Trusty, Proc. Workshop on Remote Sensing of the MarineBoundary Layer, p.5 3 (1977)

15. Particle Measurement Systems, ASASP instruciton manual

16. "Measurements of the Humidity Structure Function Parameters,2cq and c. , over the ocean", C. W. Fairall, G. E. Schacher,tqand K. L. Davidson, accepted Boundary Layer Meteorology.

90

I

17. "Naval Weapons Center Version of the Atmospheric TransmittanceComputer Code LOWTRAN: User's Manual and Program

Listing,"

W. M. Cornette, NWC Technical Memorandum 3107, 1977.

91

. . .... - ! I Ii II I I P I i

DISTRIBUTION LIST

No. of Copies

1. Defense Documentation Center 2Cameron StationAlexandria, Virginia 22314

2. Library, Code 0142 2Naval Postgraduate SchoolMonterey, California 93940

3. Dean of Research, Code 012Naval Postgraduate SchoolMonterey, California 93940

4. Dr. C. W. Fairall 4BDM Corporation, 1340 Munras St.Monterey, California 93940

5. Professor J. Dyer, Code 61DyNaval Postgraduate SchoolMonterey, California 93940

6. Professor G. J. Haltiner, Code 63HaNaval Postgraduate SchoolMonterey, California 93940

7. Assoc. Professor K. L. Davidson, Code 63Ds 4Naval Postgraduate SchoolMonterey, California 93940

8. Professor G. Schacher, Code 6lSq 10Naval Postgraduate SchoolMonterey, California 93940

9. Professor E. C. Crittenden, Code 6lCtNaval Postgraduate SchoolMonterey, California 93940

10. Dr. J. R RichterCode 532Naval Oceans Systems CenterSan Diego, California 92152

11. Dr. Lothar Rohnke 1Code 8320Naval Research LaboratoryWashington, D. C. 20375

12. Dr. D. JensenCode 5322Naval Oceans Systems CenterSan Diego, California 92152

92

13. Mr. H. HughesCode 5332Naval Ocean System CenterSan Diego, California 92152

14. Dr. J. FitzgeraldCode 8326Naval Research LaboratoryWashington, D. C. 20375

15. Mr. JeckCode 8323Naval Research LaboratoryWashington, D. C. 20375

16. Dr. G. TrustyCode 5568Naval Research LaboratoryWashington, D. C. 20375

17. Dr. A. ShlantaCode 3173Naval Weapons CenterChina Lake, California 93555

18. Dr. Barry KatzCode R42Naval Surface Weapons CenterWhite Oak LaboratorySilver Spring, Maryland 20362

19. Mr. Eugene J. MackCalspan CorporationBuffalow, New York 14221

20. Dr. R. KnollenbergParticle Measurements, Inc.1855 S. 57th Ct.Boulder, Colorado E0301

21. Mr. G. MathewsCode 1232Pacific Missile Test CenterPoint Mugu, California 93042

22. Mr. J. RosenthalCode 3253Pacific Missile Test CenterPoint Mugu, Califer--a 93042

23. CDR K. Van SiekleCode Air-370Naval Air Systems CommandWashington, D. C. 20360

93

AD-AO87 656 NAVAL POSTGRADUATE SCHOOL MONTEREY CA F/G 4/1OPTICAL AEROSOL SPECTROMETERS FACTORS AFFECTING OPTICAL EXTINCT--ETC(U)APR 80 G E SCHACHER, K L DAVIDSON

UNCLASSIFIED NPS-61-80VIS3 NL

1111L L 132i *36

MCROCOPY RESOLU106 TEST CHARTNAifONAI ROM AIil (If STAN( ARPS 14 A

24. Lt. Gary LeyPMS-405Naval Sea Systems CommandWashington, D. C. 20360

25. Dr. A. GorochNaval Environmental Research Prediction FacilityMonterey, California 93940

94

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