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IAPRS & SIS, Vol.34, Part 7, "Resource and Environmental Monitoring", Hyderabad, India,2002 
AN EMPIRICAL APPROACH FOR RETRIEVAL OF GEOPHYSICAL PARAMETERS 
FROM IRS P4 MSMR 
A.K. Varma, R. M. Gairola, Samir Pokhrel, B.S. Gohil and Vijay K. Agarwal 
Oceanic Sciences Division 
Meteorology and Oceanography Group 
Space Applications Centre, ISRO 
Ahmedabad 380015, India 
KEY WORDS: MSMR, TMI, SSM/I, Brightness Temperature, Cloud Liquid Water, Integrated Water Vapor, Ocean Surface Wind 
Speed, Sea Surface Temperature 
ABSTRACT: 
MSMR derived geophysical parameters (GPs), viz., Cloud Liquid Water (CLW), Integrated Water Vapour (IWV), Ocean Surface Wind 
Speed (OWS) and Sea Surface Temperature (SST) are available for operational use. All parameters, except CLW compare reasonably 
well with similar products from other satellites like SSM/I and TMI, and surface observations. 
In this paper, we have described development of an alternate algorithm empirically by calibrating MSMR brightness temperatures (Tbs) 
with concurrent GPs from TMI. The algorithms thus obtained have high multiple correlation of 0.82 for CLW, 0.97 for IWV, 0.78 for 
OWS and 0.89 for SST. The error of estimation is found to be 8.75 mg cm? for CLW, 0.31 gm cm? for IWV, 1.86 ms! for OWS, and 
1.81 K for SST which are within acceptable accuracies for various applications. Comparison of MSMR derived GPs with similar 
products from SSM/I is made on 2-days and monthly averaged basis and presented in this paper. 
1. INTRODUCTION 
Over last few decades, passive microwave remote sensing 
techniques have been increasingly used for studying various 
atmospheric and oceanic parameters with their all-time, quasi-all- 
weather operational capabilities. Passive microwave remote 
sensing set a major milestone with the launch of Special Sensor 
Microwave Imager (SSM/I) onboard Defense Meteorology 
Satellite Program (DMSP) satellite in 1987. SSM/I is still 
continuing on DMSP series of satellites with several (2 to 3) of 
them orbiting the earth same time. More recently, in 1999, a very 
advanced radiometer, Tropical Rainfall Measuring Mission 
(TRMM) Microwave Imager (TMI) was launched onboard 
TRMM satellite that carried 10.65, 19.35, 21, 37 and 85.5 GHz 
frequencies with all received in V and H polarizations (except 21 
GHz, received only in V polarization). 
India launched its first microwave radiometer SAMIR onboard 
Bhaskara-I satellite in 1979, and that was followed in a quick 
succession to SAMIR-II onboard Bhaskara-IlL. SAMIR-I & II 
have been extensively exploited for measuring wind speed, 
integrated water vapor and cloud liquid water over the oceans. 
After SAMIR, the Indian microwave remote sensing program 
received a major advancement, by successfully launching of 
Indian remote sensing satellite IRS-P4/ Oceansat-1 in May 1999, 
which carried a Multichannel Scanning Microwave Radiometer 
(MSMR) onboard operating at 6.6, 10.65, 18 and 21 GHz 
frequencies with dual polarizations. The brightness temperature 
(Tb) data from MSMR was used to retrieve atmospheric and 
oceanic geophysical parameters (GPs), like Integrated Water 
Vapor (IWV), Cloud Liquid Water (CLW), Ocean surface Wind 
Speed (OWS) and Sea Surface Temperature (SST) over global 
Oceans. 
In this paper, we have attempted an alternative empirical approach 
to estimate CLW, IWV, OWS and SST over global ocean from 
MSMR, using concurrent observations of TMI. TMI GP data are 
obtained from Global Hydrology Resource Centre 
(GHRC/NASA). The data set is provided at a resampled grid of 
about 10X10 km size on satellite swath over the global oceans. 
This data set contains CLW, IWV, OWS, and SST over the 
oceans, and is generated using Wentz algorithm (Wentz, 1997). 
In this study, we have further compared global maps of all GPs 
from our empirical algorithm with those from SSM/I and 
operational MSMR algorithm. 
2. OPERATIONAL MSMR GPDS 
Description of the MSMR system is provided by Mishra et al. 
(2002). MSMR brightness temperatures (Tbs) and GPs are 
generated in three resolution grids of 150, 75 and 50 km, 
respectively. The 18 and 21 GHz Tbs are available at all the grids. 
The best grid resolution at which 6.6 GHz and 10 GHz Tbs are 
available is 150 and 75 km, respectively. Derivation of CLW and 
IWV use only high frequency channels, and thus they are 
available in all three grids. OWS is available in two grids of 150 
and 75 km., with the use of all 8 channels in 150 km grid, and use 
of 6 channels in 75 km grid (without 6 GHz). Derivation of SST 
uses all 8 channels and thus is available only in 150 km grid. 
MSMR geophysical data is available day wise (24 hrs.) in three 
grids with a quality flag.