Retrieval Of Agrometeorological Parameters Using Satellite Remote Sensing Data

Agriculture and Soils Division

Indian Institute of Remote Sensing, Dehra Dun

Abstract : The recent development of satellite meteorology has allowed us to estimate spatially and frequently number of basic agro-meteorological parameters. This paper discusses approaches of retrieval of several agro-meteorological parameters viz. surface albedo, land surface temperature, evapotranspiration, absorbed photosynthetically active radiation by integrated use of optical and thermal infrared sensors satellite data.

INTRODUCTION

Countries in the Asia-Pacific region have networks of agro-meteorological ground stations in order to monitor the agricultural production and weather forecasting. But, such networks are generally less dense than they should be for a correct representation of the high spatial climatic variability which exists in Asia-Pacific region. Also the agro-meteorological data from various ground stations are not delivered in real time to a central collecting point. So, conventional agro-meteorological techniques have severe limitations to use their data for real time agricultural monitoring and yield forecasting.

The recent development of satellite meteorology has allowed us to obtain frequent and accurate measurements of a number of basic agro-meteorological parameters (e.g. surface albedo, surface temperature, evapotranspiration, solar radiation, rainfall etc.). The satellite estimated agro-meteorological parameters have several advantages compared to conventional measurements of agro-meteorological data in ground meteorological network.

Satellite Remote Sensing and GIS Applications in Agricultural Meteorology pp. 175194

• The spatial scale, from 50 m to 5 km depending on the satellite resolution, is more precise than ground climatic data (typically near 100 km for synoptic stations and 10-50 km for local less regular stations).

• High temporal data (e.g. every half an hour for METEOSAT).

• Remote sensing has access to surface agromet properties, as opposed to screen height agromet data in conventional method which attempts to characterize air mass properties.

The various approaches of retrieval of several agro-meteorological parameters viz. Surface albedo, Surface temperature, Evapotranspiration (ET), Absorbed photo-synthetically active radiation (APAR) using satellite data are discussed in following sections.

APPROACHES OF RETRIEVAL OF AGRO-METEOROLOGICAL PARAMETERS USING SATELLITE DATA

Surface Albedo

The amount of solar radiation (0.4 - 4.0 |m) reflected by a surface is characterized by its hemispherical albedo, which may be defined as the reflected radiative flux per unit incident flux. Surface albedo is an important parameter used in global climatic models to specify the amount of solar radiation absorbed at the surface. Moreover, variations in surface albedo can serve as diagnostic of land surface changes and their impact on the physical climatic system can be assessed when routinely monitored surface albedo is used in climatic models. Albedo information is useful for monitoring crop growth, prediction of crop yield, and monitoring desertification.

For clear sky conditions, the surface albedo may be estimated by remote sensing measurements covering optical spectral bands.

The albedo 'A', can generally be expressed by the following equations (Valientez etal., 1995) :

where L is the integral of the spectral irradiance weighted by the filter function of the band (W/m2/Sr) and Es is the integral of the spectral solar irradiance weighted by the filter function (W/m2).

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