Geometric Correction of NOAA AVHRR GAC Data
Kimiaki Saitoh*, Toshiaki Hashimoto** , Koji Kajiwara* and Ryutaro Tateishi*
Center for Environmental Remote Sensing(CEReS), Chiba University, Japan
1-33, Yayoi-cho, Inage-ku, Chiba 263 Japan
Basic Engineering Co.Japan
16-11, Sakae-cho, Takasaki 370 Japan
Abstract
The objective of this study is to estimate accuracy of geometrically corrected GAC data. The used geometric correction method requires just a small number of GCPs using : ephemeris data. This method is based on photogrammetric theory. 20-30 GCPs and check ; points were collected from the Digital Chart of the World(DCW) for one GAC scene which , goes around the earth with the width of about 3,000 Km.
1 Introduction
Images acquired by remote sensing have different distortion due to the earth's curvature and rotation, satellite parameters( for example, speed, attitude and altitude ), scan skew and : projection of spherical surface on a flat image. These distortions prevent meaningful r comparison among multi temporal satellite images. Therefore geometric correction includes identifying the geographic coordinates corresponding to an image pixel( Direct image referencing) and locating a pixel corresponding to given geographic coordinates( Inverse image referencing ), is essential in many remote sensing studies-
NOAA AVHRR data are widely used in weather, climate and environmental studies. A VHRR data, particularly GAC data( Global Area Coverage) data are adaptable for global environmental study. However its ephemeris data is not exact and geometric distortions ..must be removed using some GCPs. The object of this study is to correct geometric distortions using photogrammetric theory and to estimate accuracy of the geometrically corrected GAC data- Geometric correction method using photogrammetry theory
If geometric correction of NOAA A VHRR is done only by using ephemeris data from ; National Oceanic and Atmospheric Administration, the corrected image has not enough r accuracy due to ephemeris error, time error between the satellite and receiving station and t satellite attitude error. Therefore it is necessary to use GCPs. The geometric correction V method applied in this study is developed by Hashimoto and Murail) in which position andattitude of the satellite are corrected using collinearity equation of photogrammetry .
2.1 Collinearity equation
To correct the A VHRR data accurately, it is necessary to calculate the position( X
o.Y
o.Z
o)
and the attitude(
w,
F, k: roll, yaw, pitch) of the satellite exactly. Therefore we regardtheir parameters as exterior orientation parameters in photogrammetry and calculate themfrom collinearity equation. The satellite position is expressed by distance from the geocentric place(R), angle from equator plane(u), inclination angle(i), right ascension of ascending node(
W). The target earth surface is expressed by geocentric coordinate system. The Image coordinates defined the right-handed coordinate system that directionto the is satellite trace direction and direction to the z is normal direction of satellite trace. Collinearity equation here means that center of the projection( position of the sensor) andthe image point and the target earth surface is in a line.
Fig.1 Collinearity equation
