IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India,2002 
  
  
    
  
  
  
  
  
  
    
AGRICULTURAL LAND MONITORING USING THE SPECIAL SENSOR 
MICROWAVE IMAGER (SSM/I) DATA DURING 
MONSOON SEASON IN INDIA 
R.P.Singh* and V.K.Dadhwal" 
Crop Inventory and Modeling Division, Agricultural Resources Group (RESA) 
Space Applications Centre (ISRO), Ahmedabad-380015, INDIA 
( raghavendrasingh(hotmail.com, * dadhwalvk@hotmail.com) 
" Commission VII, Working Group VII/6 
KEYWORDS: Brightness Temperature, Normalized Difference Vegetation Index, Surface Wetness, Polarization 
ABSTRACT 
An exploratory study on use of passive microwave radiometer data for agricultural applications in India, aiming at (a) 
assessment of crop growth (b) crop growing environment (soil wetness) and (c) retrieval of screen air temperature was 
conducted. Horizontal (H) and vertical (V) Polarization data of 19, 37 and 85 GHz including 22 (V) GHz acquired 
from DMSP-SSM/I data during Kharif season in 1999 were analysed using both frequency difference and polarization 
difference approaches. A non-linear inverse relationship between the 37 GHz Microwave Polarization Difference 
Index (MPDI) estimated using SSM/I data and Normalized Difference Vegetation Index (NDVI) from NOAA-AVHRR 
over different crops was observed. Surface wetness index showed a characteristic increase in wetness from early kharif 
season to mid of kharif with moderate reduction again in the early stage of rabi season. Early sowing of rice in Punjab 
as well as areas affected due to flood inundation caused by super cyclone in Orissa in last week of October 1999 was 
detected. An empirical model based on linear combination of brightness temperature of four frequencies viz. 19H, 22V, 
37V and 85V was developed for retrieval of screen air temperature. Estimated temperature showed root mean squared 
error of 1.4 °C with respect to screen air temperature. The results indicated that SSM/I data, due to its daily availability 
and large coverage provides multiple inputs for monitoring of crops and their environment at regional scale. 
1. INTRODUCTION 
The temporal assessment of crop and its growing 
environment is most important for crop yield prediction 
as well as understanding the exchange of moisture and 
energy between crop and atmosphere. Passive microwave 
radiometers, although limited by coarse spatial 
resolution, have shown global applicability in assessment 
of vegetation, surface temperature and surface 
wetness/soil moisture even in the cloudy conditions. 
Most of the data from earlier microwave radiometer 
(Bhaskara-SAMIR, IRS-P4-MSMR,  Nimbus-SMMR) 
has been extensively used for atmospheric and oceanic 
applications with little attention over agricultural 
applications in India. The current and near future 
satellite observing systems such as Special Sensor 
Microwave Imager (SSM/I), Tropical Rainfall Measuring 
Mission (TRMM) microwave imager (TMI), Advanced 
Microwave Scanning Radiometer (AMSR) on EOS Aqua 
and ADEOS-II platform and proposed Soil Moisture and 
Ocean Salinity (SMOS) Mission, hold promise for soil 
moisture and temperature estimation. A number of land 
surface parameter retrieval algorithms (Basist et al, 
1996, Choudhury, 1989, Choudhury, and Tucker 1987, 
Lakshmi et al. 1997) have been proposed for these 
sensors, which need evaluation/ validation over Indian 
region. This paper reports an exploratory study to 
evaluate the SSM/I radiometer data for estimation of 
three important parameters viz. crop growth, surface 
wetness and minimum screen air temperature during 
Kharif season on regional scale in India. The Microwave 
Polarization Difference Index (MPDI) (Owe et al. 2001) 
using 37 GHz was used for crop assessment. Multi- 
channel approach based on the principle of differential 
emissivity reduction from high to low frequencies with 
wetness was adopted to assess the surface wetness 
condition (Basist et al. 1998). The information obtained 
from surface wetness index was used to assess the sowing 
of rice on regional scale. A regression analysis between 
SSM/I channels (19H, 22V, 37V and 85V) and minimum 
screen air temperature obtained from India 
Meteorological Department (IMD) observations was 
carried out (McFarland et al. 1990) for temperature 
estimation. These parameters can be used as inputs in 
coarse resolution models of soil —vegetation-air transfer 
(SVAT) models as well as for large scale crop 
assessment. 
2. STUDY AREA AND DATA USED 
The brightness temperatures of 19, 37, 22 and 85 GHz 
from the descending passes of SSM/I radiometer onboard 
Defence Meteorological Satellite Program (DMSP) —F13 
satellite were used in study during June 1999 to 
November 1999 over India. SSM/I is a canonical 
scanning microwaves radiometer system flown in near 
circular, sun-synchronous, and near polar orbit, with an