WMOD00548

• Contract/Permit #: 6-07-DR-20020
• Project Name: Sierra Cooperative Pilot Project
• Title: Satelite Studies During the 1976-77, 1977-78 Sierra Cooperative Pilot Project
• Date: 2/1/1979
• Weather Modification - Doc Type: Report

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B. Navigation of Satellite Imagery
Small perturbations in the orbit of the nearly geostationary

satellite cause features on the earth as seen by the satellite to

drift through periodic displacement as the orbit progresses. Most of

this movement is removed during the data transmission by using a set

of parameters which describe the orbit. In this manner, a computerized

grid is sent within the data stream so that features on the image can

be located relative to the earth. The error in the location of this

grid is often quite large, as is seen by comparing landmarks visible

on the image to the grid position. This gridding, along with the use

of landmarks, was used to co-locate the images and determine the posi-

tion of the Sierra Project target area within them for the 1976-77 data

set. When no landmarks were visible, in particular during the night

when only IR images are available, the grid was the only way to navi-

gate the first year's data. For the 9 March 1977 case study in this

report, the grid appeared to be accurate to within 5 to 10 km.

A more accurate navigation is possible by using line documentation

recorded at the beginning of each line of IR data in the 1977-78 data

set. This method requires a satellite attitude to be determined by

making landmark location measurements in terms of latitude and longi-

tude on the earth, and line and element on the satellite image.

Analytic navigation routines (Smith, Phillips, 1972) then give a "best

fit" set of orbital parameters which combine with the scan number of

the satellite VISSR to navigate the data in the line (north-south)

direction. A "beta" parameter, which is derived by sensing the sun's

and earth's edges by the satellite, is included in the line documentation,

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