Recalibration of DMSP SSMI/S for Weather and Climate Applications

Transcription

1 Recalibration of DMSP SSMI/S for Weather and limate pplications Banghua Yan NO/NESDIS/OR & QSS Group Inc. and Fuzhong Weng NO/NESDIS/OR he 15 th International OVS Studies onference, Maratea, Italy, October 3 10, 2006

2 SSMI/S haracteristics and Data History

3 (Weng et al, SI ) Major Impediments for MW Imager/Sounder nomalous emission from unknown targets Warm load instability and solar and stray slight contamination alibration uncertainty from instrument non-linearity Difficult to characterize the radio frequency interference in particular wavelengths Scan dependency due to intrusion of Glare Suppression System-B Pre-launch characterization, antenna patterns, brightness temperature standard, and well characterized target Difficult to correct for satellite orbit drift in trend analysis

4 SSMIS ntenna System and ntenna Emission Main-reflector conically scans the earth scene Sub-reflector views cold space to provide one of two-point calibration measurements Warm loads are directly viewed by feedhorn to provide other measurements in two-point calibration system he SSMIS main reflector emits radiation from its coating material SiOx VD (coated vapordeposited aluminum) SiOx and l VD Mixture Graphite Epoxy ' = + ε R ( R )

5 FF nalyses of Warm ounts (54.4 GHz) Warm load calibration is contaminated by solar and stray Lights Reflection Off of the anister op into Warm Load Direct Illumination of the Warm Load ines WF = FF -1 ( FF(W) * Filter(f L ) ) ), where f L is a cutoff frequency of the low pass filter, where 102 minutes.

6 SSMIS alibration lgorithms 1. Use the emissivity from NRL antenna model and the temperature measured from the thermister mounted on antenna arm as an approximation 2. nalyze the time series of warm load counts together with PR and define the anomaly locations in terms of the FF harmonics 3. nalyze the time series of cold space view count and define the anomaly locations in terms of the FF harmonics and cosmic temperature plus antenna correction ' Δ c = (1 ε ) + = = = W ' ε 1 ε Δ Δ W R where is the antenna temperature corresponding to the earth scene s radiance, and ε R and R is the reflector emissivity and emperature, respectively W W R R ε R R Δ R + W Δ W

7 SSMIS ntenna emperature Bias February 3, 2006 (a) Before anomaly correction (b) fter anomaly correction 54.4 GHz 54.4 GHz emperature biases from DR and SDR space are related through the slope coeff. for spill-over correction, b = a*a + b Δ = ΔB / a

8 SSMIS Bias rending

9 MSU vs. SSMIS Matching through Simultaneous onical Overpass SNO every pair of POES satellites with different altitudes make orbital intersections within a few seconds regularly in the polar regions (predictable w/ SGP4) Precise coincidental pixel-by-pixel match-up data from radiometer pairs provide reliable long-term monitoring of instrument performance he SNO method (ao et al., 2005) is used for on-orbit long-term monitoring of imagers and sounders (VHRR, HIRS, MSU) and for retrospective intersatellite calibration from 1980 to 2003 to support climate studies he method has been expanded for SSM/I with Simultaneous onical Overpasses (SO) 54.4 GHz 55.5 GHz

10 Non-Linear lgorithm SSMI/S SO Distribution Non-linear calibration equation: S SL 2 = + S( ) + μs ( )( ) = + μz, where = S + S( S ), S = W W S S, Z = S 2 W ( S SL )( S W ) For SO observations between two sensors (K,J): (a) Over North Pole Δ SL, N + ( μk Z K, N μj Z J, N ) = 0 (in North Pole: sea ice only) Δ SL, S + ( μk Z K, S μj Z J, S ) = 0 (in South Pole: land only) (b) Over South Pole

11 F-10 vs. F-13 SSM/I SO Matching (37-85 GHz hannels)

12 Preliminary Evaluation of Non-Linearity erm in F13 and F15 (a) Non-linearity parameter (μ) (b) Non-linearity term (Q = μz) S = SL + μz

13 Rader alibration Beacon Interference in F15 SSM/I GHz Due to Radcal Beacon interference 23 ORREION (K) Descending Node" scending Node

14 otal Precipitable Water (PW) from F15 (& F13) SSM/I F15 PW (beacon signal contaminated) F15 PW (beacon signal removed) omparison of F15 PW (B removed) with F13 PW F13 PW

15 Scan Dependant Biases F8 F10 F11 F13 F14 F15 F16 onclusion: Rapid fall-off 1~3 K at (B) near end (sometimes at the beginning) of scan.

16 Summary. SSMIS ntenna emission and warm load anomaly: the NESDIS/SR beta-version of the SSMIS calibration algorithm has significantly eliminated most of SSMIS radiance anomalies. Nonlinearity : a new algorithm to derive SSMI non-linear parameter has been developed. It is found that the nonlinearity of SSMI radiances is still important. However, more tests are needed. Radar calibration Beacon interference: a beta version of the algorithm has been developed in NESDIS/SR which can remove the Beacon signal from F GHz. Scan dependency: there is a rapid fall-off 1~3 K at (B) near end (beginning) of scan primarily due to intrusion of Glare Suppression System - B.

17 Scan Dependant Biases F8 F10 F11 F13 F14 F15 F16 onclusion: Rapid fall-off 1~3 K at (B) near end (sometimes at the beginning) of scan.

18 On-Going Plans: SSMI/S DR/SDR/EDR lgorithm Flow RDR DR DR (Semi-) Empirical orrection lgorithm Modules ntenna Emission orrection alibration arget nomaly orrection Nonlinear alibration Scan Dependency orrection RFI (e.g., Beacon Interference) orrection RDR DR SDR alibration arget nomaly orrection Orbit Drift orrection EDR EDR Empirical/ Physical lgorithm Modules Heritage EDR lgorithms New EDR lgorithms (e.g., ε, s ) SDR EDR

19 Backup

20 he First SSM/I Monthly Products Generated from NO/NESDIS

21 DMSP and NO onstellation s of ugust N 0000 DMSP LNs F F F F N18 N16 F N15 N17 F15 F14 F16 NO LNs N N N N

22 Microwave Instrument alibration Energy sources entering feed for a reflector configuration 1. Earth scene omponent, 2. Reflector emission 3. Sensor emission viewed through reflector, 4. Sensor reflection viewed through reflector, 5. Spacecraft emission viewed through reflector, 6. Spacecraft reflection viewed through reflector, 7. Spillover directly from space, 8. Spillover emission from sensor, 9. Spillover reflected off sensor from spacecraft, 10. Spillover reflected off sensor from space, 11. Spillover emission from spacecraft omponents

23 omparison of otal Precipitable Water (PW) between F15 and F13 Before Beacon signal is removed fter Beacon signal is removed S S DS DS