MICROWAVE REMOTE-SENSING PROJECT UPDATEgsics.atmos.umd.edu/pub/Development/20140826/Dave...Aug 26, 2014 · o David Zacharias, ZAX Millimeter Wave Company . Electromagnetics Division

Electromagnetics Division

MICROWAVE REMOTE-SENSING PROJECT UPDATE

Presentation to GSICS Microwave Sub-Group, 26 August 2014

David WalkerElectromagnetics Division

NIST, Boulder, CO


Contributors Technical Staff--NIST FTPs:

o Kevin Coakley, Statistical Engineering Div.

o Mike Francis, Electromagnetics Div.

o Joshua Gordon, Electromagnetics Div.

o Jeff Guerrieri, Electromagnetics Div.

o Mike Janezic, Electromagnetics Div.

o David Novotny, Electromagnetics Div.

o Jolene Splett, SED-ITL

o David Walker, Electromagnetics Division

Technical Staff--NIST Associates:

o Dazhen Gu, (RA at CU-CET, ECEE Dept.)

o Derek Houtz (Graduate PREP, CU Aerospace Dept.)

o Jim Randa (Associate Prof., CU Physics Dept.)

o Ron Wittmann (NIST Associate; retired)


Collaborators (partial list)

o Bill Blackwell, MIT-LL

o David Draper, Ball Aerospace Corp.

o Prof. Bill Emery, CU Aerospace Engineering Dept.

o Prof. Al Gasiewski, CU-CET Director

o Ed Kim, NASA GSFC

o Paul Racette, GSFC

o David Zacharias, ZAX Millimeter Wave Company


OUTLINE

• Current research topics:

• Brightness-temperature (Tb) standards

• Standard radiometer

• Standard target

• Ocean salinity standards

• Robotic antenna range (CROMMA facility)

• Advanced radiometer calibration methods

• Summary & plans

• NB: Tb and GPS-RO traceability


Radiometric Target Measurement

--Use existing NIST radiometer linked to primary noise standards (SI Traceable):

NIST Noise Radiometer + Characterized Antenna

Rad.

Std.

Ant.

Cryo

Amb

C

a

x

0Target

Rad.

Std.

Ant.

CryoCryo

AmbAmb

C

a

x

0TargetTarget

Primary Standards


Waveguide 6-port reflectometerwith heterodyne receiver

Waveguide banded radiometers

Primary Noise Standards


Thermal Noise Primary Standards

• Ambient & cryogenic (liquid nitrogen) standards.

uTCry 0.65 K

uTAmb 0.1 K

◄Coaxial

Waveguide►


Setup for Target Reflectivity Characterization and Brightness Temperature Calibration

• NIST anechoic chamber

• K-band pyramidal horn attached to NIST radiometer

• 13-inch target from NASA

2.68(68)

1.1(28)


Target Reflectivity• Reflectivity lower than 40 dB in K-band (18-26 GHz), inline with

the specification of the target.

• Negligible difference between hot and ambient conditions.

• Validated by different hardware and measurement conditions

• Developing full emissivity char. with robotic range


Target reflection characterization at 183 GHz, performed at CU-CET


Achievable Uncertaintywith Standard Radiometer (only)

Goal is to reach the accuracy requirements for climate change study:

NIST

radiometerTroposphere Stratosphere Precipitation

Water

vapor

Sea

surface

temp

u ~ 0.7-1.0 K 0.5 K 1 K 1 K 1.25 K 0.03 K

Ref: “Stability and accuracy requirements for satellite remote sensing instrumentation for global climate monitoring,” ISPRS 2004.


Transfer NIST Tb cal to instrument radiometer

antenna

anechoic chamber

targetNISTRadiometer

antenna

anechoic chamber

targetInstrumentRadiometer

Note: Geometry mustbe maintained in xfer

Transfer pre-launch cal to on-orbit cal: background change can be accommodated

antennatargetInstrument

Radiometer

SpaceEnvironment


Anti-sun (y)

Nadir (z)

Velocity (x)

70x60x40 cm

End Point: SI-Traceable calibration of ATMS pre-launch and on-orbit


Standard Radiometer vs. Standard Target

Independent realizations of TB

Independent, full uncertainty analyses

Combined (full) standard would be a weighted average of the two

Possible √2 uncertainty improvement vs. single std.

Transferring the TB standard would involve either:

A second (portable) target calibrated with the full standard

Measuring a customer’s target or radiometer at NIST with the full standard


Black Body Targets--Current DesignConstrained volume and mass for space and

aircraft calibration

large temperature gradients

Up to 0.6 K mean offset from recorded temp

Narrow optimal operating frequency range due to periodic pyramid structure

0 0.01 0.02 0.03 0.04 0.050

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

z (m)

r (m

)

346.5

347

347.5

348

348.5

349

349.5

Cox, A.E. et al. “Initial Results from the Infrared Calibration and Infrared Imaging of a Microwave Calibration Target” Int. Geoscience and Remote Sensing Symposium, Denver 2006.

Gu, Dazhen. “Reflectivity Study of Microwave Blackbody Targets” Trans. on Geoscience and Remote Sensing, vol. 49, No. 9, Sept. 2011.


Proposed Design

single open conical or folded cone structure

Uniform emissivity ≈ 1 over broad microwave frequency spectrum (10-200 GHz)

Reduction in temperature gradients

Hot and cold source with water or LN2 circulation

absorber (Eccosorb or thin layer of microwave similar)

Aluminum substrate

Copper fluid circulation tubing


Std Target--Thermal Modeling

Steady state temperature field using uniform empirical heat transfer coefficients

0.06 K offset between aluminum substrate and mean radiating surface

ANSYS 3D finite element solution 2D heat equation solution of cross section

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

z (m)

r (m

)

Steady State Temperature 1 mm absorber 10 cone

349

349.1

349.2

349.3

349.4

349.5

349.6

349.7

349.8

349.9

350

0.88 0.9 0.92 0.94 0.96 0.98

-0.18

-0.17

-0.16

-0.15

-0.14

-0.13

z (m)

r (m

)

Steady State Temperature 1 mm absorber 10 cone

349

349.1

349.2

349.3

349.4

349.5

349.6

349.7

349.8

349.9

350


CFD – Conjugate Heat Transfer Analysis

Full computational fluid dynamics simulation of blackbody in anechoic chamber

Determine heat transfer coefficients on specific geometries

Forced convection on blackbody from cooling fans in chamber

Investigate insulations

Inlet and outlet fans in chamber stabilize background temperature

Velocity streamlines of the fluid solution. This allows precise calculation of convection coefficient field across target


Electromagnetic Modeling

First order physical/geometric optics (PO) calculation

Calculate reflectivity (infer emissivity) from multiple bounces inside structure

Runs quickly to compare absorber types

High Frequency Structural Simulator

Commercial full wave EM solver)

Finite element method, high accuracy

Runs on 16 processor 130 GB RAM HPC

~1 hour per frequency point solution

θ0

θ1

1

Г01

Air (k0)

Absorber

(k1)

Aluminum T

01

T10

Г10

T10

Δd

Г10

-1

-1

Considerations for single bounce on absorber material inside cone

HFSS models, ¼ cropped at symmetry axes, (left) mesh example, (right) folded cone example


Target calibration/test chamber

Temperature MonitoringElectronics

WaveguideRadiometer

CryogenicNoise

Standard

Ambient Noise

Standard

Horn

Target

MountingPlate

Temperature ControlAnd Alignment Systems

Temperature Sensors

Absorber

Housing

Air circulator

Air Circulator

Waveguide Switch


Bench-Top Anechoic Chamber

Electromagnetics DivisionMain Beam

On-Earth Sidelobes

Accurate antenna pattern measurementsand pattern correction algorithms areessential to environmental datarecord (EDR) retrievals.


Robotic Range• >180º meas. range• Laser tracker

provides dynamic positioning error correction of 22 µm (λ/50 @ 270 GHz)

• Able to accommodate up to 1 m3 and 30 kg mass; e.g., ATMS-sized instrument

• 110-183 GHz Operational

• Up to 500 GHz capability with existing hardware

• Ideal for CubeSat-type instruments

See the video! http://nist.gov/pml/electromagnetics/rf_fields/robot-arm-aids-antenna-calibration.cfm


Scattering (BRDF) Measurements

We are using the CROMMA to measure bi-static and mono-static reflections from the NIST black-body target.

Range of measurable target reflectivity: 0 to -60 dB.

Limited by system losses (30 dB) and dynamic range (90 dB).

Target is at the center of the scanning arc, illumination is aligned to the center of rotation.


Summary & Plans

• TB standard radiometer demonstrated at NIST

• Initial development 18-26.5 GHz band; 12 to 65 GHz now, with plans to build 75-110 GHz rad.

• Next: Demonstrate practical cal. transfer to flight instrument, FY15/FY16

• Primary standard target

• Potential reduction in uncertainty (goal ~0.25-0.5 K)

• Provides a means for checking and transfer

• Modeling & design nearing completion

• Fabricate & test target FY15-16

• Ocean salinity


GPS-RO and Tb Standards• GPS-RO is SI-traceable through freq. stds.

• Still requires modeling to get to T, H

• Only at 1.2 and 1.6 GHz

• Spatial coverage: 8-25 km alt., 300 km area, ~1 km height resolution

• Creates reliable long-term RO data record

• Radiometry can be SI-traceable with Tb stds.

• No modeling for T (for known ε); other EDRs not so

• Broad freq. coverage: 1-65 GHz now, more (higher) soon

• Creates reliable long-term Tb data records

• Comparable uncertainties achievable with GPS-RO or radiometry; ~1 K (single retrieval)

Documents

MICROWAVE REMOTE-SENSING PROJECT UPDATEgsics.atmos.umd.edu/pub/Development/20140826/Dave...Aug 26, 2014 · o David Zacharias, ZAX Millimeter Wave Company . Electromagnetics Division