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IAPRS & SIS, Vol.34, Part 7, "Resource and Environmental Monitoring". Hyderabad, India,2002
SURFACE INSOLATION RETRIEVAL FROM GEOSTATIONARY SENSOR
B. K. Bhattacharya , M. R. Pandya, A.S.Nain and V. K. Dadhwal*
Crop Inventory and Modelling Division
Agricultural Resources Group, RESA
Space Applications Centre (ISRO) 380015, India
* Commission VII, Working Group VII/6
KEYWORDS: METEOSAT, Atmospheric precipitable water, Atmospheric turbidity, cloud optical properties
ABSTRACT:
A study was carried out to retrieve and validate surface insolation under clear and cloudy sky conditions by a physical approach
using visible and thermal band data from geostationary satellite over Indian sub-continent. Meteosat data of Indian ocean coverage are
acquired for five acquisitions at 7:00, 10:00, 12:00, 14:00 and 17:00hrs. IST during 1st to 30th December 1998. A total of 150 images
per band were analysed to produce daily and five day average total insolation output over India. Sensitivity analysis of insolation for
different atmospheric input parameters, total precipitable water, Angstrom turbidity parameters was carried out.The retrieved
insolation when compared to estimates from BSS measurements over six Indian stations (Hissar, Karnal, Pune, Pantnagar, Faizabad
and Patancheru) indicated a mean absolute bias (MAB) of 1.89 and 1.76 MJm? for daily and five day average insolation estimates
respectively.
1. INTRODUCTION
Insolation received at ground surface is one of the important
inputs to crop simulation models for estimating regional NPP
and study on energy and water balance, in a number of
disciplines covering agro- forest ecology and global climatic
change studies. Before reaching the ground, the solar radiation
undergoes absorption and scattering processes with the
atmospheric constituents such as: ozone, water vapor, mixed
gases and aerosol. The downward solar radiation reaching the
ground is composed of two components, a diffuse radiation
component from the sky dome after scattering and absorption in
atmosphere and direct radiation reaching earth with least
interference by the atmospheric constituents. Ground-based
measurements of insolation are generally made with
pyranometers located at weather stations and agricultural
experimental stations. These stations are too sparse to provide
representative spatial variation of insolation from conventional
meteorological observations such as: Cloud cover, cloud type,
cloud height, bright sunshine hours (BSS) precipitable water and
temperature.
The feasibility of deriving and mapping surface insolation from
satellite data has been investigated elsewhere using a number of
approaches including regression based (Brakke and Kanemasu,
1981), numerical (Gautier et al., 1980), physical (Rigollier and
Wald, 1999 & 2000; Tanahashi et al., 2001) and DEM based
(Wang et al, 2000) techniques tested with geostationary
satellites such as: Meteosat, Europe and VISSR GMS-5, Japan,
GOES, NASA as well as polar orbiting satellites such as:
Landsat TM and NOAA AVHRR data. A preliminary study
with limited clear sky Meteosat data (Bhattacharya et al., 2002)
showed that the surface insolation could be retrieved with higher
accuracy over Indian sub-continent using physical approach
* Corresponding author: bkbbhatt@yahoo.com
than regression and semi-physical approaches. Among the
different physial models used in the recent past, the algorithm
used by Tanahashi ef al. (2001) has some advantages over
others. It takes account of atmospheric correction in great
details. Both direct and diffuse components of insolation can be
derived using this model. The present study is aimed at
retrieving and validating surface insolation using Meteosat data
of Indian Ocean coverage for both clear and cloudy skies using a
physical approach.
2. STUDY AREA AND DATASETS
The Indian Ocean coverage of METOSAT-5 images both in
visible (2.5kmX2.5km) and thermal (5km X 5km) bands were
acquired from EUMETSAT covering 7 °- 38° N to 68-100 E
(1338 line X 1442 pixels) for the period I" to 30" December
1998. Time of acquisitions were 7.00, 10.00, 12.00, 14.00 and
17.00 hrs. IST. In all, a total of 150 images per band were
acquired for analysis. All Meteosat images were coregistered
with INSAT 2E CCD visible band. The daily total insolation
derived from Bright Sunshine Hours (BSS) method for the
corresponding period were obtained for validation purposes
over six stations in India. These stations are: Hissar (29°10'N,
75%4'E), Karnal (29°42'N, 77°02'E), Pune (18°32'N, 73%51’E),
Pantnagar (29°N, 79°50/E), Faizabad (26°15/N, 82°08'E) and
ICRISAT, Patancheru (77°21'N, 78°01'E). The image processing
and analysis were carried out using ENVI 3.4 version image
processing software and IDL 5.3 programming language.