IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring", Hyderabad, India,2002 
  
METHODOLOGY DEVELOPMENT FOR IN-FLIGHT CALIBRA TION AND 
EVALUATION OF HIGH RESOLUTION REMOTE SENSING SENSORS USING 
ARTIFICIAL CALIBRATION SITE 
A.K.Shukla* and P.R.Nair# 
* Mailing address : SIIPA,Space Applications Center(ISRO),Jodhpur Tekra,Ahmedabad-380 053,India. 
Email : akshukla@ipdpg.gov.in 
# Mailing address : SPL, Vikram Sarabhai Space Center(ISRO),Thiruvananthapuram-695 022,India. 
KEY WORDS : Vicarious calibration, Radiative transfer, Artificial targets, Optical depth, CHHARODI, SATCOR 
ABSTRACT: 
In-flight calibration of spacecraft remote sensing sensors after launch is essential to evaluate the performance of sensor in orbit over 
its mission life. Normally, these sensors are pre-flight calibrated in the laboratory and data products are generated using pre-flight 
calibration coefficients and supplied to user community. Over a period of time, there has been a requirement to monitor sensor 
performance periodically and suggest changes in calibration coefficients if any, so that better calibrated data products could be used 
by the users. Also, it is possible to inter-compare the sensor data once radiometrically calibrated data are available from each sensor. 
This paper presents an approach for end-to-end calibration of remote sensors in orbit using reflectance based vicarious calibration 
technique. The procedure involves three main components namely, correction of sensor digital counts using in-house designed and 
developed atmospheric correction algorithm, design and development of a controlled calibration test site with artificial targets and 
use of calibrated instruments for ground/target reflectance measurement and aerosol/ozone/water content measurements during 
synchronous data collection with each satellite pass. Details of radiative transfer algorithms, design aspects of the calibration site 
developed locally along with results based on in-situ measurements carried out with IRS satellite passes are presented in this paper. 
1. INTRODUCTION 
Reflectance based vicarious calibration technique is very 
useful for in-flight calibration of spacecraft sensors. Using this 
technique, it is possible to carry out absolute radiometric 
calibration as well as inter-comparison of one sensor data with 
other data. Today, satellite remote sensing has grown to a good 
stage of maturity with many operational sensors in the orbit. 
The entire mechanism of data processing algorithms are well 
developed to convert raw data into meaningful and useful 
geophysical quantities for a large number of applications. 
Efforts are continuing to improve the accuracy of retrieved 
parameters. With growing awareness among user community 
about the accuracy of information, the need for calibration and 
validation is well established. As per CEOS objectives, the goal 
has now shifted to the availability of data sets to users which 
are transparent and independent of any sensor characteristics. 
Certain applications such as agriculture and monitoring natural 
disaster, benefit from the increasing number of remote sensors 
in operations. To compare data from several sensors having 
different spatial resolution and spectral bands, it is desirable for 
some applications and essential for others, to know how the 
response of the sensors compare (Rao & Chen,1995). Such 
comparisons can be made relatively, but more dependable if 
referenced to an absolute scale .Another important need for in- 
flight calibration arises from the launch and post launch effects. 
Earth observation satellite sensors have been susceptible to 
significant post launch changes in their performance 
characteristics. These changes arise as a result of many factors, 
including the rigors of the launch itself, the space environment 
in the earth orbit in general, the operating environment of the 
spacecraft, and the aging of the sensors and their subsystems. 
Thus even a well built stable and well characterized sensors 
require evaluation and monitoring of changes in the months 
immediately following launch especially but also over the life 
time of their operation (Teillet, 1997). 
  
This paper presents the complete methodology developed 
recently at Space Applications Center for high resolution IRS 
sensors such as, LISS-3, LISS-4 and PANCHROMATIC 
cameras. Reflectance based approach for vicarious calibration 
has been evolved using the theory of Radiative transfer of 
electromagnetic radiation passing through the atmosphere. 
Operational procedures have been developed based on 
synchronous calibration campaigns conducted on CHHARODI 
calibration site with IRS satellite passes. Details of each 
components along with sensor parameter evaluation are 
presented in this paper. 
2. REVIEW OF METHODS FOR IN-FLIGHT 
CALIBRATION 
Radiometric calibration of sensor is carried out in two ways, 
relative and absolute. Relative calibration is done by 
normalizing outputs of the detectors of a CCD to a given often 
averaged output from all the detectors in the spectral band. In 
this way, all the detectors of CCD array give the same output 
when the focal plane of the sensors is irradiated with a uniform 
light source. The source need not be calibrated. Absolute 
calibration is performed by ratioing the digital count output 
from a sensor with the value of an accurately known uniform 
light source. Three types of absolute radiometric calibration are 
possible : preflight laboratory calibration using standard source, 
in-flight calibration using on-board source and in-flight 
vicarious calibration using known ground targets. Pre-flight 
calibration of sensors are done against the calibrated light 
sources whose spectral characteristics are well known and 
traceable to NIST primary source. These type of exercises are 
done after integration of payloads and light transfer 
characteristics (LTC) curves are generated for each spectral 
band and calibration coefficients are generated which are used 
in the data product generation. These are called Pre-flight 
calibration coefficients. Few sensors have been flown with on- 
    
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