Abstract

GPS for Digital Satellite Image Correction


D. Vijaya Lakshmi
Associate Professor
VNR Vignana Jyothi Institute of Engg & Tech,
Email: psridhar_babu_2k@yahoo.com

Dr. I.V. Murali Krishna
Professor
JNTU, Hyderabad
Email: ivm@ieee.org



Modern GPS technology provides location data with an accuracy of plus and minus five meters. Traditional use of GPS for geometric correction of satellite imagery aims to establish the relationship between the image coordinate system and a geographic coordinate system. In doing so, errors inherited within satellite data can be calibrated and reduced as well. The systematic errors in GPS are caused by many factors that can be summarized as multi path, atmosphere, position dilution of precision (PDoP), imprecise orbit, and the clock. Theoretically, systematic errors can be reduced using spatial statistics.
Errors found in applied GPS to geometric correction of digital satellite imagery and air photography can be related to systematic errors and the geodetic and projection systems used. The GS systematic errors can not be eliminated, nevertheless, they can be reduced. For example, most available GPS provides a visual representation of satellite location on the sky making it possible for the user to check for PDoP. Multipath effect can be reduced in an open sky areas. Still the remaining errors are a problem and can be reduced using Differential GPS (DGPS). The recent development in space age technology such as in IKONOS and Quick Bird has provided digital imagery with a resolution as high as 25 centimeters. Most available digital imagery comes with or with out coordinate system. All GPS data were collected using latitude/longitude readings in the form of degree, minutes, and decimal seconds (DD, MM, SS.SS). The standard errors as expected are in the decimeter level and estimated at 22 centimeters in the Easting direction and 23 centimeters in the Northing direction. The study suggests a maximum error on the entire image to be 3.54 meters on the Easting direction and -2.3 on the Northing direction. The maximum RMS is 3.59 meters . When the reference point checked for accuracy, the point location was about 1.94 meters from where it should be.