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

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. Components of Tb as Measured by SFMR

8. 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).

9. 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

10. SFMR factory calibration • Calculation of Tb • Table of calibration constants

11. 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

12. 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

13. SFMR Pod effect

14. 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

15. 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

16. 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]

17. SFMR