March 8, 2005March 8, 2005

Calibration and Operation of the Stepped Calibration and Operation of the Stepped Frequency Microwave RadiometerFrequency Microwave Radiometer during the 2005 Hurricane Season during the 2005 Hurricane Season

Ivan PopStefanija Ivan PopStefanija popstefanija@prosensing.compopstefanija@prosensing.com Mark GoodberletMark Goodberlet goodberlet@prosensing.comgoodberlet@prosensing.com

ProSensing Inc. ProSensing Inc. 107 Sunderland Rd. 107 Sunderland Rd.

Amherst, MA 01002 USA,Amherst, MA 01002 USA, www.prosensing.comwww.prosensing.com

2005 Hurricane season2005 Hurricane season

April 21, 2023April 21, 2023

SFMR 2005 SFMR 2005 accomplishmentsaccomplishments

May 2005: Delivery of the third SFMR, S/N US003May 2005: Delivery of the third SFMR, S/N US003

June 2005: Delivery of the retrofitted SFMR, S/N US002June 2005: Delivery of the retrofitted SFMR, S/N US002

July 2005: Successful testing of upgraded SFMR (implementation of July 2005: Successful testing of upgraded SFMR (implementation of

the “cold” calibration load)the “cold” calibration load)

August 2005: Validation of the new SFMR for wide range of August 2005: Validation of the new SFMR for wide range of

environmental conditions (TS to CAT 5) in comparison with the environmental conditions (TS to CAT 5) in comparison with the

original “IWRS” SFMRoriginal “IWRS” SFMR

August 2005: First time deployment of two SFMR’s operating on August 2005: First time deployment of two SFMR’s operating on

N43RF (N43RF (SFMR-US003SFMR-US003) and N42RF () and N42RF (SFMR-US002SFMR-US002))

2005 July-November: Spare SFMR (US001) available (down time for 2005 July-November: Spare SFMR (US001) available (down time for

replacement – about 4 hours)replacement – about 4 hours)

2005 June-November: Flawless operation of SFMR Hardware2005 June-November: Flawless operation of SFMR Hardware

April 21, 2023April 21, 2023

SFMR Development HistorySFMR Development History

• [[1970s1970s] Concept of airborne ] Concept of airborne measurements of ocean surface winds measurements of ocean surface winds developed at NASA Langleydeveloped at NASA Langley

• [[1982-19951982-1995] Prototype SFMR, designed ] Prototype SFMR, designed by the University of Massachusetts, by the University of Massachusetts, tested by NOAA HRD and AOCtested by NOAA HRD and AOC

• [[1995-20011995-2001] SFMR-HRD built by ] SFMR-HRD built by ProSensing (formerly Quadrant ProSensing (formerly Quadrant Engineering) funded by OFCM through Engineering) funded by OFCM through IWRS programIWRS program

• [[20012001] ProSensing developed a compact ] ProSensing developed a compact SFMR installed in an external aircraft pod SFMR installed in an external aircraft pod (funded by NRL) (funded by NRL)

• [[20032003] ProSensing delivered a wing-pod ] ProSensing delivered a wing-pod mounted SFMR to NOAA, funded by OFCMmounted SFMR to NOAA, funded by OFCM

• [[20042004] Real-time wind estimates ] Real-time wind estimates provided by SFMR impact NHC hurricane provided by SFMR impact NHC hurricane forecastsforecasts

SFMR-HRD (IWRS)SFMR-HRD (IWRS)

SFMR-AOCSFMR-AOC

April 21, 2023April 21, 2023

SFMR AOC Validation SFMR AOC Validation • SFMR-IWRS and SFMR #US003 SFMR-IWRS and SFMR #US003

installed on N43RF for installed on N43RF for simultaneous and independent simultaneous and independent operationoperation

• Comparative operation and data Comparative operation and data collection through Katrina flights collection through Katrina flights capturing the full range of capturing the full range of environmental conditions: TS,CAT1, environmental conditions: TS,CAT1, 3, 4,and 5 3, 4,and 5

TS CAT 3 CAT 5 CAT 4

SFMR 2005 SFMR 2005 accomplishmentsaccomplishments

April 21, 2023April 21, 2023

SFMR Theory of OperationSFMR Theory of Operation

• The Stepped Frequency Microwave The Stepped Frequency Microwave Radiometer is designed to measure Radiometer is designed to measure blackbody electromagnetic radiation of the blackbody electromagnetic radiation of the scene at six frequencies (4 to 6 GHz)scene at six frequencies (4 to 6 GHz)

• Measured power is expressed as Measured power is expressed as brightness temperature which is a function brightness temperature which is a function of the physical temperature of the scene of the physical temperature of the scene and its emissivity (0<emissivity<1)and its emissivity (0<emissivity<1)

• The frequency dependence of the The frequency dependence of the brightness temperature is used to brightness temperature is used to estimate wind speed and rain rate estimate wind speed and rain rate

April 21, 2023April 21, 2023

SFMR Theory of OperationSFMR Theory of Operation

• Measured TMeasured TB B is affected is affected by a variety of by a variety of environmental factorsenvironmental factors– Extra terrestrial radiationExtra terrestrial radiation– Atmospheric vapor and Atmospheric vapor and

liquidliquid– Ocean SalinityOcean Salinity– Sea surface temperatureSea surface temperature– Physical temperature of Physical temperature of

ocean and atmosphereocean and atmosphere– Ocean surface roughnessOcean surface roughness

April 21, 2023April 21, 2023

Components of TComponents of Tb b as Measured by as Measured by SFMR SFMR

0

50

100

150

200

250

Bri

gh

tnes

s T

emp

erat

ure

( K

)

1 2 3 4

Condition Code

SFMR, 4.74 GHz

Solar

Cosmic

Atmosphere, Downwelling

Atmosphere, UpWelling

Ocean, Rough

Ocean, Calm

0

50

100

150

200

250

Bri

gh

tnes

s T

emp

erat

ure

( K

)

1 2 3 4

Condition Code

SFMR, 6.02 GHz

Solar

Cosmic

Atmosphere, Downwelling

Atmosphere, UpWelling

Ocean, Rough

Ocean, Calm

0

50

100

150

200

250

Bri

gh

tnes

s T

emp

erat

ure

( K

)

1 2 3 4

Condition Code

SFMR, 7.09 GHz

Solar

Cosmic

Atmosphere, Downwelling

Atmosphere, UpWelling

Ocean, Rough

Ocean, Calm

April 21, 2023April 21, 2023

SFMR SFMR CalibrationCalibration

• A “two-load” technique is used A “two-load” technique is used to achieve a to achieve a calibratedcalibrated measurement of measurement of TTaa

• Measurement accuracy is Measurement accuracy is unaffected by changes in the unaffected by changes in the radiometer receiver radiometer receiver characteristicscharacteristics

• Internal calibration tracks Internal calibration tracks short term SFMR drifts short term SFMR drifts (performed 100 times per (performed 100 times per second)second)

• Internal loads do not account Internal loads do not account for changes in antenna for changes in antenna characteristics (i.e., it is a characteristics (i.e., it is a receiver-only calibration). receiver-only calibration).

DetectorDiode

T1

TA

T2

Receiver:

Gain = GR Bandwidth = B

Noise Temp = T R

GV

VB

V

S1

S2

T c cA 0 1

V V

V V

T T

TA1 0

2 1

2

1

V k B G T T G VR A R V B0 ( )

BVRR VGTTGBkV )( 21

BVRR VGTTTGBkV )( 212

April 21, 2023April 21, 2023

SFMR Calibration with External SFMR Calibration with External LoadsLoads

• External loads, viewed via the radiometer External loads, viewed via the radiometer antenna, are used for a “total system” antenna, are used for a “total system” (receiver + antenna) calibration(receiver + antenna) calibration– Warm Load: Absorber box with continuously Warm Load: Absorber box with continuously

monitored physical temperaturemonitored physical temperature– Cold Load: Cloudless sky at nightCold Load: Cloudless sky at night

• External calibration is primarily used to External calibration is primarily used to characterize antenna characteristicscharacterize antenna characteristics

• External calibration at factory is performed External calibration at factory is performed once a yearonce a year

April 21, 2023April 21, 2023

SFMR factory calibrationSFMR factory calibration• Calculation of TCalculation of Tbb

}35

{353535 32

25

5410

LLB

taa

ta

ta

taaT

• Table of calibration constantsTable of calibration constants

SFMRUS003

F04.74 GHz

F15.31 GHz

F25.57 GHz

F36.02 GHz

F46.69 GHz

F57.09 GHz

a0 276.21 287.38 270.19 255.65 284.64 290.81

a1 37.66 23.77 34.12 65.77 49.28 14.82

a2 -304.79 -303.55 -274.90 -253.07 -135.24 -138.41

a3 -34.19 -21.00 -25.55 -31.64 -23.60 3.81

a4 -2.549 -3.418 -3.881 -4.075 -4.731 -4.343

a5 2.146 0.763 1.488 -0.701 -3.427 -1.125

April 21, 2023April 21, 2023

Flight CalibrationFlight Calibration

• In-flight calibration of SFMR is performed In-flight calibration of SFMR is performed by flying over a buoy or by using by flying over a buoy or by using dropsondes.dropsondes.

• In-flight calibration is needed to account In-flight calibration is needed to account for biases due to reflections and emissions for biases due to reflections and emissions from external objects (i.e. instrument pod, from external objects (i.e. instrument pod, aircraft engine)aircraft engine)

• Measurement bias is estimated and Measurement bias is estimated and adjustments are reported to AOCadjustments are reported to AOC

• 2005 calibration flight on July 18 in TS 2005 calibration flight on July 18 in TS IreneIrene

April 21, 2023April 21, 2023

SFMR Pod EffectsSFMR Pod Effects• It is desirable to It is desirable to

eliminate the need for eliminate the need for in-flight calibrationin-flight calibration

• In-flight test should In-flight test should only be used as a pre-only be used as a pre-season system checkseason system check

• ProSensing built a ProSensing built a mock-up pod to mock-up pod to determine the effects determine the effects of the pod on SFMR of the pod on SFMR datadata

April 21, 2023April 21, 2023

SFMR Pod effectSFMR Pod effect

-50

-40

-30

-20

-10

0

-180 -120 -60 0 60 120 180

Off Broadside Angle ( degs )

Am

plit

ud

e (

dB

) 4.74

5.31

5.57

6.02

6.69

7.09

-50

-40

-30

-20

-10

0

-180 -120 -60 0 60 120 180

Off Broadside Angle ( degs )

Am

plit

ud

e (

dB

) 4.74

5.31

5.57

6.02

6.69

7.09

2

3

4

5

6

7

8

100 200 300 400 500 600 700 800

Time ( s )

Sky

Brig

htne

ss T

empe

ratu

re (

K )

April 21, 2023April 21, 2023

Measurement of Wing Pod Measurement of Wing Pod Effects on SFMR dataEffects on SFMR data

• Antenna beam patterns showed negligible Antenna beam patterns showed negligible changechange

• Calibration with external loads (with and Calibration with external loads (with and without pod mock up) showed significant without pod mock up) showed significant difference of about 0.7 Kdifference of about 0.7 K

• Difference in the actual configuration Difference in the actual configuration could be higher. could be higher.

• Recommendation: re-design bottom plate Recommendation: re-design bottom plate of the wing podof the wing pod

April 21, 2023April 21, 2023

Proposed “Zero-Zero” Proposed “Zero-Zero” calibrationcalibration

• Flight calibration conditionsFlight calibration conditions– Wind speed < 5 m/sWind speed < 5 m/s– No precipitationNo precipitation– Cloudless skyCloudless sky– Night flight – no possibility of sun glint Night flight – no possibility of sun glint

(up to 12 K bias)(up to 12 K bias)– Fly over buoy at multiple altitudes Fly over buoy at multiple altitudes

April 21, 2023April 21, 2023

Future SFMR WorkFuture SFMR Work

• Test and debug the newly-developed SFMR 2005W rack Test and debug the newly-developed SFMR 2005W rack mounted computer and interface boxmounted computer and interface box

• SFMR software upgrades to improve operation robustness:SFMR software upgrades to improve operation robustness:– Real time input data [TReal time input data [Tbb ] quality check ] quality check– Real-time land mask to eliminate reporting of invalid dataReal-time land mask to eliminate reporting of invalid data– Real-time check of the RMS error of the wind retrieval modelReal-time check of the RMS error of the wind retrieval model– In flight self-calibration with minimal operator involvementIn flight self-calibration with minimal operator involvement

• Analyze 2005 Analyze 2005 HurricaneHurricane season data to improve wind retrieval season data to improve wind retrieval model in some ranges of operationmodel in some ranges of operation– Low wind speed (<15 m/s)Low wind speed (<15 m/s)– Rain height estimate (important at wind speeds lower then 20 m/s)Rain height estimate (important at wind speeds lower then 20 m/s)– Analyze high wind conditions (above 50 m/s) [HRD: Uhlhorn, Black] Analyze high wind conditions (above 50 m/s) [HRD: Uhlhorn, Black]

April 21, 2023April 21, 2023

SFMSFMRR