ALOS Data Users Handbook

ALOS Data Users Handbook7.1.3 Orbit DataIn addition to the conventional orbit data of RARR, ALOS uses the GPSR data on the spacecraft and theprecision orbit data generated from this GPSR data conducting off-line processing at ground.Table 7.1-3 describes the definition and precision about the orbit data to be used in the rocessing subsystem.Onboard orbit data Low ratemissiondataTable 7.1-3 Orbit Data TypeType From Definition Content CoordinatesystemCentral of Absolute positionGPS antenna Absolute speed 1PPSphase reference time clock biaseALOS precisionorbit data (ECI)ALOS precisionorbit data (ECR)ALOS conventionalorbit data(definitive) (ECI)ALOS conventionalorbit data(definitive) (ECR)ALOS conventionalorbit data(predictive) (ECI)ALOS conventionalorbit data(predictive) (ECR)Time Interval Accuracy When it isSystemusedEmergencyprocessingWGS-84*1 GPS 1 sec. 200m(95%)GYTS Satellite Position data speed data TOD UTC 60 sec. Less than Routinebarycenter1m processingditto ditto ditto ITRF97 ditto ditto ditto dittoFDS ditto ditto TOD ditto ditto 150m (3σ) GPS data isnot availableditto ditto ditto True Earth fixedcoordinatesystem *2ditto ditto ditto dittoditto ditto ditto TOD ditto ditto 3 days later1 km (3σ)ditto ditto ditto True Earth fixed ditto ditto ditto dittocoordinatesystem *2Emergencyprocessing*1 Since differences between WGS-84 and ITRF97 are very small, they are treated as the same coordinate inthe processing subsystem, and transformation between two coordinates is not taken into account.*2 Since differences between true Earth fixed coordinate system and ITRF97 are very small, they are treatedas the same coordinate in the processing subsystem, and transformation between two coordinates is nottaken into account.7.1.4 Attitude DataThe premise of the ALOS attitude data is as follows:1) There are two kinds of onboard attitude determination systems, one is a precision attitudedetermination system and the other is a standard attitude determination system.2) In the standard attitude determination system, the attitude data is output by three-axis attitude angle(roll, pitch, and yaw) to the orbital coordinate system. This coordinate system is generated bypropagating in the satellite. The orbit model of it is not downlinked.3) In the precision attitude determination system, the attitude data is output even if this data isquaternion. This quaternion is the one which shows the rotation between the satellite coordinatesystem and ECIJ2000), and the reference coordinate system is ECI (J2000).7-5