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2005 Hurricane season. Calibration and Operation of the Stepped Frequency Microwave Radiometer during the 2005 Hurricane Season. Ivan PopStefanija popstefanija@prosensing.com Mark Goodberlet goodberlet@prosensing.com ProSensing Inc. 107 Sunderland Rd.
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2005 Hurricane season Calibration and Operation of the Stepped Frequency Microwave Radiometer during the 2005 Hurricane Season Ivan PopStefanija popstefanija@prosensing.com Mark Goodberletgoodberlet@prosensing.com ProSensing Inc. 107 Sunderland Rd. Amherst, MA 01002 USA,www.prosensing.com
SFMR 2005 accomplishments May 2005: Delivery of the third SFMR, S/N US003 June 2005: Delivery of the retrofitted SFMR, S/N US002 July 2005: Successful testing of upgraded SFMR (implementation of the “cold” calibration load) August 2005: Validation of the new SFMR for wide range of environmental conditions (TS to CAT 5) in comparison with the original “IWRS” SFMR August 2005: First time deployment of two SFMR’s operating on N43RF (SFMR-US003) and N42RF (SFMR-US002) 2005 July-November: Spare SFMR (US001) available (down time for replacement – about 4 hours) 2005 June-November: Flawless operation of SFMR Hardware
SFMR Development History SFMR-HRD (IWRS) • [1970s] Concept of airborne measurements of ocean surface winds developed at NASA Langley • [1982-1995] Prototype SFMR, designed by the University of Massachusetts, tested by NOAA HRD and AOC • [1995-2001] SFMR-HRD built by ProSensing (formerly Quadrant Engineering) funded by OFCM through IWRS program • [2001] ProSensing developed a compact SFMR installed in an external aircraft pod (funded by NRL) • [2003] ProSensing delivered a wing-pod mounted SFMR to NOAA, funded by OFCM • [2004] Real-time wind estimates provided by SFMR impact NHC hurricane forecasts SFMR-AOC
SFMR 2005 accomplishments SFMR AOC Validation • SFMR-IWRS and SFMR #US003 installed on N43RF for simultaneous and independent operation • Comparative operation and data collection through Katrina flights capturing the full range of environmental conditions: TS,CAT1, 3, 4,and 5 TS CAT 3 CAT 5 CAT 4
SFMR Theory of Operation • The Stepped Frequency Microwave Radiometer is designed to measure blackbody electromagnetic radiation of the scene at six frequencies (4 to 6 GHz) • Measured power is expressed as brightness temperature which is a function of the physical temperature of the scene and its emissivity (0<emissivity<1) • The frequency dependence of the brightness temperature is used to estimate wind speed and rain rate
SFMR Theory of Operation • Measured TB is affected by a variety of environmental factors • Extra terrestrial radiation • Atmospheric vapor and liquid • Ocean Salinity • Sea surface temperature • Physical temperature of ocean and atmosphere • Ocean surface roughness
SFMR Calibration • A “two-load” technique is used to achieve a calibrated measurement of Ta • Measurement accuracy is unaffected by changes in the radiometer receiver characteristics • Internal calibration tracks short term SFMR drifts (performed 100 times per second) • Internal loads do not account for changes in antenna characteristics (i.e., it is a receiver-only calibration).
SFMR Calibration with External Loads • External loads, viewed via the radiometer antenna, are used for a “total system” (receiver + antenna) calibration • Warm Load: Absorber box with continuously monitored physical temperature • Cold Load: Cloudless sky at night • External calibration is primarily used to characterize antenna characteristics • External calibration at factory is performed once a year
SFMR factory calibration • Calculation of Tb • Table of calibration constants
Flight Calibration • In-flight calibration of SFMR is performed by flying over a buoy or by using dropsondes. • In-flight calibration is needed to account for biases due to reflections and emissions from external objects (i.e. instrument pod, aircraft engine) • Measurement bias is estimated and adjustments are reported to AOC • 2005 calibration flight on July 18 in TS Irene
SFMR Pod Effects • It is desirable to eliminate the need for in-flight calibration • In-flight test should only be used as a pre-season system check • ProSensing built a mock-up pod to determine the effects of the pod on SFMR data
Measurement of Wing Pod Effects on SFMR data • Antenna beam patterns showed negligible change • Calibration with external loads (with and without pod mock up) showed significant difference of about 0.7 K • Difference in the actual configuration could be higher. • Recommendation: re-design bottom plate of the wing pod
Proposed “Zero-Zero” calibration • Flight calibration conditions • Wind speed < 5 m/s • No precipitation • Cloudless sky • Night flight – no possibility of sun glint (up to 12 K bias) • Fly over buoy at multiple altitudes
Future SFMR Work • Test and debug the newly-developed SFMR 2005W rack mounted computer and interface box • SFMR software upgrades to improve operation robustness: • Real time input data [Tb ] quality check • Real-time land mask to eliminate reporting of invalid data • Real-time check of the RMS error of the wind retrieval model • In flight self-calibration with minimal operator involvement • Analyze 2005 Hurricane season data to improve wind retrieval model in some ranges of operation • Low wind speed (<15 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]