ALOS Data Users Handbook

ALOS Data Users Handbook7.2 Optical Sensors7.2.1 Processing FlowThe outline of the data processing for PRISM and AVNIR-2 is described as follows.(1) Scene framingThe time of the scene center is recalculated using scene ID, scene shift, and orbit data.(2) Judgment of time systemThe time system status is extracted from the system telemetry within the specified time by threshold from thetime of the scene center calculated by the scene framing. Depending on the number of the extracted timesystem status, the time system is decided by its majority. At this time, time error information is used totransform the time from the ground time to the spacecraft time.As a result of the majority, only in case where the time system is decided to the GPS, by using the TAI-UTCincluded in the coordinate transformation information, the time of the scene center is re-transformed to thespacecraft time. According to this result, processing is carried out using a decided time system; if it isdecided as the GPS time system, its time system is regarded as the GPS. If the DMS time system is decidedthe processing is as well.(3) Line generationAn extension processing is carried out to the range to be determined by the time of the scene center and thenumber of the extracted lines, and the image data per CCD (in case of PRISM) or per band AVNIR-2) aregenerated. Obtain the time data added in the JPEG header in Level 0 and output them.The VCDU frame loss, the JPEG frame loss, and saturation rate can be obtained during this processing.(4) Pre-processingThis processing checks the orbit data, the attitude data and the telemetry data.a) Primary check of the Level 0 image and the imaging time determinationThe preliminary check of the extended image is carried out and the relation equations between imaging timeand line number are determined.7-7