Differential O2 Absorption Barometric Pressure Radar (DIAR_BAR):

Improvements in Tropical Storm Forecasts

Qilong Min1, Bing Lin2, Yongxiang Hu2 , Wei Gong1, Steven Harrah2, Wes Lawrence3, Dion Fralick2,

1State University of New York, Albany, NY

2NASA Langley Research Center, Hampton, VA3Old Dominion University, Norfolk, VA

Spatial coverage: very limited Costs: high Uncertainty: ~1 mb

Existing techniques: in-situ

drift buoy

moored buoy

dropsonde

No remote sensing technique is available.

Sea surface pressure measurements

Atmospheric pressure : the primary driving force for atmospheric dynamics and generates wind fields that transport mass, moisture and momentum.

Historical studies

• Active & passive O2 A-band instruments

active: high stable laser system --- difficult

passive: daytime, cloud free, aerosol loading

• Microwave sounder

25 ~ 75GHz: multiple channels (6)

absorption: LW, WV

atmospheric and cloud temperature

footprints, sea surface reflectivities

Oxygen is uniformly mixed in the atmosphere, and attenuates the transmitted signal – less at lower freq. and more at higher freq.

The amount of attenuation is directly related to

barometric pressure and altitude.

f or 1/GHz)

PPRecRec

Atten

uation

Calibrated PRec

w/o Attenuation

Aircraft/Spacecraft-BasedQ-Band (50-56GHz) Radar

Measurement Concept

Pr () = PTAe2(, )0(, , )/(4R2()) (1)

Pr: radar received power; T: transmittance

() exp (OLV) = exp (OOLLVV) (2) where O = MP0/g, M: mixing ratio; P0: sea surface pressure

Pr(1)/Pr(2)=C(1)C(2)-1exp(-2 (O(1)-O(2))MOPO/g). (3) power ratio of two frequency channels at the O2-band

Similar LW & WV absorption (50~56GHz)

Almost the same in footprint & reflectivity

P0 C0(1, 2) + C1(1, 2) loge(Pr(1)Pr-1(2)) (4)

A very simple near-linear relationship between surface air pressure and radar

power ratio of two different frequencies (or differential absorption index) is expected from the O2 band radar data.

Theoretical basis

Radar simulated results

Most of the variability is due to global atmospheric profile variations: temperature, water vapor, clouds, etc.

PoC Instrument Development

Agilent8362BPNA

50-56 GHz Transceiver

15 GHx PLOX 5 = 45GHz

Port 1

Port 2

10 MHz Ref

5-11 GHz IF

5-11 GHz IF 50-56 GHz

TransmitAntenna

ReceiveAntenna

5-11 GHz IF

5-11 GHz IF

15 GHz PLO

50-56 GHz

Agilent8362BPNA

50-56 GHz Transceiver

15 GHx PLOX 5 = 45GHz

Port 1

Port 2

10 MHz Ref

5-11 GHz IF

5-11 GHz IF 50-56 GHz

TransmitAntenna

ReceiveAntenna

5-11 GHz IF

5-11 GHz IF

15 GHz PLO

50-56 GHz

Agilent 8362BNetwork Analyzer

SpaceK Labs 45GHz Up/Down

Converter

Quinstar 24"Cassegrain Antennas

Ground tests

Radar Installed in/on Mobile Radar Lab

relatively isolated radar reflector

• nearly spherical reflector• ~300m clear range

ProjectedBeamwidth

Varina-Enon BridgeI-295 South of Richmond, VA

Approx. 150’ above James River

Ground tests

Measure Water NRCS Over Wide Inc. Ang.Support Satellite Design

Supported by VDOT

PATAUXENT RIVER NAVAL AIR STATION

Flight tests

Observed and simulated Differential absorption

LEO SatelliteInstrument

• COTS & Lab Equip.• Demo Concept

• Operational Design• Op. Perf. Assessment• Technology Readiness

Level from 3 to 7

• GlobalMeasurements

15 ~ 22 km

0 – 3 km >220 kmAirborne

Instrument

Proof-of-ConceptInstrument

Technology Roadmap

Sea level pressure (SLP) assimilation (WRF)

“Simulated satellite SLP” using surface pressure measurements during first landing of Katrina

Model configuration

Advanced Research WRF (ARW) dynamic solver

CCM3 Radiation

Thompson cloud microphysics and Kain-Fristch convective parameterization

Mellor-Yamada PBL

36 and 12 km horizontal resolution and 28 layers, 261×181 grid mesh

84 -hour simulation

276 278 280 28224

25

26

27

28

29

30

276 278 280 28224

26

28

30

Case Assimilation Pattern Scale Length Factor

CTL No

Ga Area 0.25-1.00

Gl Lowest Pressure 0.25-1.00

Gc Area without lowest pressure 0.25-1.00

Gb A 2 degree band 0.25-1.00

Sea level pressure (SLP) assimilation (WRF)

e

f

987 993 999 1005 1011 1018 1024

276 278 280 28224

25

26

27

28

29

30

987 993 999 1005 1011 1018 1024

276 278 280 28224

25

26

27

28

29

30

987 993 999 1005 1011 1018 1024

276 278 280 28224

25

26

27

28

29

30

987 993 999 1005 1011 1018 1024

276 278 280 28224

25

26

27

28

29

30

987 993 999 1005 1011 1018 1024

276 278 280 28224

25

26

27

28

29

30

987 993 999 1005 1011 1018 1024

276 278 280 28224

25

26

27

28

29

30

OBS

NCEP-FNL

Gl_.25

Gl_1.0

Ga_.25

Ga_1.0

Sea-Level Pressure at 00 UTC August 26, 2005

Sea level pressure (SLP) assimilation (WRF)

CTL Gl(.25) Ga(1.0)

Ga(1.0)-CTLGl(.25)-CTL

•The assimilation runs symmetrically strengthen the cyclonic flow and enhances the westward and southward mean flow.

•Due to deepening of the hurricane vortex, the convective heating is enhanced

Initial column wind vector (m/s) in the experiments

Ga

Hurricane Katrina tracks

• Single point assimilations have large spread in track when different length scales are used

• All points assimilations have small spread in track and produce close track and landing position

Gl

Thick Black soild—best estimateBlack dashed—CTLSensitivity to scale length factorBlack –1; Red—0.75; Green—0.5 and Black—0.25

900

920

940

960

980

1000

26 27 28 29

Date

Min

SL

P (

hP

a)

Gl(.25)

Gb(.75)

Gc(1.0)

Ga(1.0)

best

12km

30

60

90

120

150

26 27 28 29

Date

Max

Win

d (

Kn

ots

)

Gl(.25)

Gb(.75)

Gc(1.0)

Ga(1.0)

best

12km

Hurricane Katrina Intensity (84-hour: Gl, Ga, Gc and Gb)

Without center pressure, Gc simulates comparable results as Ga, indicating the effect of pressure horizontal distribution in assimilation.

Exp(36km)

Distance (km)

Minimum Pressure (hPa)

Maximum Wind (Knot)

CTL 360 24 49

Ga 71 7 26

Gl 120 11 28

Gb 38 6 28

Gc 66 9 27

Summary

The differential O2 absorption pressure radar will provide the first remote sensing barometric data! The accuracy of instantaneous surface air pressure measurements could be ~4mb. (grid averages: errors ~1mb)

Lab, ground, and flight tests of current prototype instrument indicate that it works

Next generation radar: operational capability This effort will lead significant improvements in predictions of

hurricane intensities and tracks.

This differential O2 absorption radar technique may dramatically extend the current, limited-point barometric capability over oceans with airborne and spaceborne instruments.