In the program of geolocation with environmental meteorological satellite

the earth location software makes use of earth ellipsoid and terrain surface data in conjunction with satellite orbit parameter and geometry attitude

and information of the sensor and satellite geometry to compute data including geodetic longitude and latitude coordinates

height

ground to satellite direction vector and range

and solar vector.The satellite orbit propagation model and the mathematical procedure which intersects the sensor’s line of sight with the terrain surface of the Earth are most important in the program.In order to meet the requirement of high precision geolocation for environmental satellite remote sensing data

we have developed a new generation orbital motion forecast and remote sensing geolocation software system.This system is based on the variable order

and stepsize orbital motion numerical integration model（DE/DEABM）

and is different from conventional Brouwer perturbation analytical model.During the research of this system

we have studied variety of perturbations that affect orbital motion.These perturbations are pronounced for satellite at low altitudes.We use high order precise EGM-96（Earth gravity model） data to improve computing precision of perturbation for asphericity of the Earth.What we put into consideration also includes the perturbation that arises from the gravitational attraction of the Sun and the Moon

solar radiation pressure and atmospheric drag in our works.As case studies

we develop Earth location algorithms and software for two sensors

one is FY-1D VIRR launched on May 2002

and the other is FY-3A MERSI which will be launched in early 2008.In the progress

we analyse details of the optics geometry coordinates relationship of detector

focal plane

main optics system and scan mirror

which are key parts of sensors.As a result

the precision of coordinates transformation model have been developed in this software.After several days of data computing of orbital motion and Earth location test for FY-1D VIRR

we find that the precision of the new software system reaches the range from centimeters to meters.It is a great improvement compared with the 1km precision of old perturbation analytical method.Overall

it is found that the software system of FY-1D VIRR can provide navigation accuracies of within 1 km at nadir.