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meter is also similar to sun photometer but has five different 
wavelengths than Sun photometer. First three filters are 2.4nm 
bandwidth optical filters of center wavelengths 305.5,321.5 and 
320.5nm are used to compute total ozone content in Dobson 
unit Two IR channels at 935 and 1020nm with 10nm 
bandwidth provide total vertical water vapor content. 1020nm 
channel provides aerosol optical depth also. Necessary 
algorithms for all parameter computation are stored in the 
handheld instrument which provide real time computation and 
display. Calibration set ups have been developed in 
collaboration with National Physical Laboratory, New Delhi for 
Radiance/irradiance calibration of ASD spectro-radiometer. 
This instrument has been calibrated upto +/- 1.596 error on 
absolute scale. Wavelength calibration of spectro-radiometer is 
performed using spectral line sources of mercury, zinc. sodium 
and cadmium. 
7. RESULTS OF CALIBRATION CAMPAIGN WITH 
SATELLITE PASS 
CHHARODI calibration site has been used for conducting 
synchronous experiments with IRS-1C, IRS-1D and 1 mtr. 
resolution satellites. These exercises have been done to 
establish methodologies for operational data collection on the 
site. The experiments have given good experience for handling 
calibration site and artificial targets prior to satellite pass. 
Sampling methodology for collecting reflectance of bare soil 
and targets was worked out to have sufficient number of data 
points for deriving average reflectance of the soil/target. 
Though ASD spectro-radiometer is a portable instrument, it has 
to be used as back mounted by the operator with 1.5 mtr. 
length fibre optic cable. Due to large size of site ( 300mx300m 
) and targets, enough time is involved in collecting data, 
reaching from one point to another and covering the complete 
area by walk. It was estimated that almost one hour was 
required to collect one set of data for reflectance. During this 
period, sun intensity changes due to variation in solar zenith 
angle. Hence, it was decided to take spectralon reference 
measurement with each reflectance measurement of the target 
so that reflectance obtained is accurate. As far as irradiance and 
AOD measurements were concerned, samples at five minute 
interval were collected for one hour duration before and after 
satellite pass. Data at one minute interval were also collected 
using ASD and MICROTOPS instruments +/- 10 minutes 
satellite pass time and were operated simultaneously. Prior to 
data collection in operational mode, a large number of 
experiments were conducted in SAC campus to establish the 
accuracy and repeatability of both instruments. 
CHHARODI calibration site data of 25" November,1999 was 
analyzed for inter-comparison of PANCHROMATIC sensors 
of IRS-1C and IRS-1D. This day was unique as both satellite 
passes took place at an interval of 20 minutes. The weather was 
very stable and clear during the period of experiment. The 
computed radiance difference of the bare soil between two 
sensors was found to be 2.6% for a radiance value of 7.5 
mw/cm?/sr/um thus showing a very good stability of both 
sensors. Experiments with bare soil of calibration site were 
conducted again during the period from November,2000 to 
April,2001 with IRS-1C and IRS-1D passes. The Four dates 
for IRS-1D are : 9" Nov.2000,23" Jan,2001,14'^ Mar.,2001 and 
8" Apr,2001 and three dates for IRS-1C are : 19" 
Nov,2000,13" Dec,2000 and 23Feb,2001. On all these days, 
the weather during synchronous experiments was very good. 
Based on the analysis conducted for these dates, it was found 
that IRS-1D sensors showed better calibration accuracy as 
IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring", Hyderabad, India,2002 
compared to IRS-1C sensors. However, overall: RMS 
calibration errors obtained were within +/- 7.5% for all 
spectral bands of IRS-1C and IRS-1D sensors. Recently on 11" 
December,2001, vicarious calibration experiments were 
conducted on the calibration site with 1 mtr. resolution satellite 
pass using newly constructed artificial targets. The absolute 
calibration error found for this PANCHROMATIC sensor 
using 17% reflectance target is 3.7%. Detailed analysis using 
other artificial targets is being done at the time of preparing of 
this paper and they will be reported in the symposium. 
Effective resolution of the sensor has been determined using 1 
mtr. size targets and it is found to be 1.6 mtr. in along track 
direction and 1.4 mtr. in across track direction. Square wave 
response and modulation transfer function determined from the 
artificial targets are found to be within sensor specifications. 
Detailed results will be presented in the symposium. More 
experiments are also planned to be conducted using these 
targets in future. 
8. CONCLUSIONS 
This paper presents an end-to-end procedure for vicarious 
calibration and evaluation of spacecraft sensors in orbit. Due to 
limited size of artificially created calibration site and targets, 
the site is found adequate for calibrating high resolution sensors 
onboard IRS series satellites in future. The multi-point 
calibration is possible with the present approach for sensors 
with ground resolution of 6 meter or better. Various artificial 
targets developed on the site are found very useful for absolute 
calibration of 1 mtr. high resolution sensor as well as its 
parameter evaluation. The experiments conducted on the 
CHHARODI calibration site has given good experience and has 
opened up many possibilities of carrying out controlled 
experiments for sensor calibration/evaluation using small 
targets. It is planned to use this calibration site operationally for 
“ future IRS cal/val activity in SAC. 
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Mc Cartney,E.J.,1976. Optics of the atmosphere, John Wiley & 
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Nair P.R.and Krishna Moorthy K., 1997. Effect of physical 
properties of atmospheric aerosol on path radiance. 
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Rao C.R.N. and Chen J.1995. Inter-satellite calibration for the 
visible and near-infrared channels of the Advanced very high 
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Santer R. et.al,1992.SPOT calibration at La Crau test site. 
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Shukla A.K.et.al.,1994. SATCOR - An Atmospheric correction 
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Slater P.N. et. al,1987. Reflectance and radiance based 
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Turner and Spencer,1972. Atmospheric model for the 
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Teillet P.M.1997. A status overview of Earth observation 
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