# Presentation: 265861

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

**Ivan PopStefanija **_**[popstefanija@prosensing.com](mailto:popstefanija@prosensing.com)**_
**Mark Goodberlet**  _[goodberlet@prosensing.com](mailto:goodberlet@prosensing.com)_
**ProSensing Inc. **
**107 Sunderland Rd. **
**Amherst, MA 01002 USA,** _[www.prosensing.com](http://www.prosensing.com/)_

**2005 Hurricane season**

- March 8, 2005

## 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

- March 8, 2005

## SFMR Development History

- [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-HRD (IWRS)

- SFMR-AOC

- March 8, 2005

##  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 2005 accomplishments

- March 8, 2005

## 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

- March 8, 2005

## 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

- March 8, 2005

## Components of Tb as Measured by SFMR  

- March 8, 2005

## SFMR Calibration

- A “two-load” technique is used to   achieve a *calibrated* measurement of *T**a*
- 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).

- March 8, 2005

## 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

- March 8, 2005

## SFMR factory calibration

- Calculation of Tb

- Table of calibration constants

| SFMR
US003 | F0
4.74 GHz | F1
5.31 GHz | F2
5.57 GHz | F3
6.02 GHz | F4
6.69 GHz | F5
7.09 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 |

- March 8, 2005

## 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

- March 8, 2005

## 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

- March 8, 2005

## SFMR Pod effect

- March 8, 2005

## 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

- March 8, 2005

## 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

- March 8, 2005

## 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]

- March 8, 2005

## SFMR

- March 8, 2005