1. # A51I-3155
Sensitivity of Forward Radiative Transfer Model on Spectroscopic Assumptions and Input Geophysical Parameters at 23.8 GHz and 183 GHz Channels and its impact on Inter-calibration of Microwave Radiometers. by
Saswati Datta1,2, W. Linwood Jones2, Hamideh Ebrahimi2, Ruiyao Chen2, Viviene Payne3, and Rachael Kroodsma4 1 contacting author: Data and Image Processing Consultants (DIPCON), Morrisville, NC;
2: CFRSL, University of Central Florida, Orlando, FL; 3: Jet Propulsion Laboratory, California Institute of Technology; 4: ESSIC, University of Maryland College Park
Overview
Intend to check the sensitivity of the RTM to
Input WV profile Used GDAS and ECMWF Reanalysis as 2 different source of geophysical parameters
Different emissivity model : Elsaesser model and another method developed by RSS is compared. The RSS model is developed mostly for the imager channels, hence emissivity model sensitiivty is done for 23.8 GHz channel only
Different absorption model: Rosenkranz absorption and MonoRTM are used.
To test the RTM sensitivity, the single difference between observed and simulated radiances are compared for each case.
Intend to inter compare GPM microwave Imager (GMI) radiances to MT-SAPHIR, METOPB-MHS and NPP ATMS observations.
For radiometric intercalibration, used the double difference technique developed at UCF.
All data are collocated over 1°x 1° latitude longitude grid before analysis.
Theoretical values are obtained modeling the entire bandwidth with steps= 100 MHz
GDAS Vs. ERA : SAPHIR-ATMS
183 GHz results
23.8 GHz results (Note: near 23.8 GHz imaging channels used and for AMSR2-TMI and F17-TMI vicarious cold cal technique used , Kroodsma Et. al, 2014,)
ROSENKRANZ Vs. MonoRTM
DD sensitivity to different Surface Emissivity
Instrument Pair
Elsaesser Model
RSS Model
AMSR2-TMI
4.10
4.07
F17:SSMIS-TMI
2.33
2.30
GMI-TMI
1.50
1.49
Data Filters
Convection Filter: each channel should be at least 1K warmer than the one above and eliminates any matched pair for which any of the channel observed and simulated Tb’s differ more than 10 K.
0< CLWGDAS < 0.1
Only clear scenes over ocean are considered for this study
DD sensitivity near 183 GHz to different absorption model and input data
GMI-SAPHIR
Absorption Model
GDAS
RETR
Diff
GMI
183.3 ±3.0 GHz
ROSENKRANZ
-0.41
-0.51
0.10
MonoRTM
-0.89
-0.96
0.07
0.48
0.45
183.3 ±7.0 GHz
-0.53
-0.56
0.03
-0.98
-1.00
0.02
0.44
DD sensitivity near 23.8 GHz to different absorption model and input data
Instr. Pair
Absorption Model
GDAS
ERA
Diff
AMSR2-TMI
ROSENKRANZ
4.10
4.27
-0.17
MonoRTM
4.61
4.76
-0.15
-0.51
-0.49
F17:SSMIS-TMI
2.33
2.68
-0.35
2.11
2.46
0.22
DD sensitivity to different wv profile at 183 GHz
Instr. Pair
Center Frequency
GDAS
ERA
Diff
GMI-SAPHIR
-1.26
-1.45
0.19
-1.79
-1.89
0.10
ATMS-SAPHIR
2.88
1.79
1.09
1.84
0.95
0.89
2.13
1.33
0.80
1.58
0.99
0.59
Summary:
At 23.8 GHz and 183 GHz , the DD is sensitive to choice of the absorption model and also to the input wv profile. The choice of surface emissivity model does not affect the calibration much.
GDAS seem to differ from retrieved or ERA profile closer to the surface and at higher altitudes. As a result the corresponding channels closer to the surface ( SAPHIR channel 6) and very high up (channel 1 and 2) show more sensitivity to input profiles.
Profile sensitivity is also prominent in the latitudinal transect.
For SAPHIR-ATMS case, sensitivity is found to be as high as 1K.
GDAS Vs. ERA : GMI-SAPHIR
Acknowledgement: This work at UCF is supported by NASA award # NNX13AH48G