Development and calibration-of the airborne three-line scanner (TLS) imaging system

The Airborne Three-Line-Scanner (TLS) imaging system has provided proof of the concept of stereo and multispectral mapping using the pushbroom mode because frame digital imaging systems with comparable coverage and resolution have not been available and are not likely to be available in the future. A prototype of the TLS system, the STARIMAGER, was developed jointly in 2000 by the STARLABO Corporation of Japan and the University of Tokyo and is introduced in this paper. A laboratory method and algorithm to evaluate the optical characteristics of STARIMAGER are presented. The principle is to measure the object-space angles of a sufficient number of CCD elements in two directions as seen through the optics. These angular measurements reflect the real camera geometry of both the optics and the CCD arrays. A mathematical model based on the central perspective projection has been constructed to estimate the focal length, principle point, and lens distortion of the optics and the alignment errors of the CCD sensors in the focal plane. These calibration parameters have been used in several real test flights, and ground point determination accuracies from 0.03- to 0.08-m (0.5- to 1.5-pixels) in planimetry and from 0.06- to 0.15-m (1.2- to 3-pixels) in elevation from a flying height of 500 m were attained.