Takanori Iwata

Precision attitude and position determination for the Advanced Land Observing Satellite (ALOS)

The Advanced Land Observing Satellite (ALOS) is required to achieve stringent attitude determination accuracy (3.0×10-4deg on-board and 1.4×10-4deg ground-based), position determination accuracy (1m ground-based), and attitude stability (3.9 × 10-4deg/5sec) in order to provide precise geometric accuracy for high-resolution images without ground control points. It is designed to yield the geolocation determination accuracy of 6m from attitude and position estimates and that of 3m with an additional high-bandwidth measurement. Presented in this paper are ALOSs platform and ground systems technologies developed for achieving the attitude determination accuracy and the position determination accuracy. They include a precision star tracker, optimal attitude estimation algorithms (real-time and off-line), an alignment change reduction, a jitter sensor, a precision GPS receiver, and a ground-based position estimation algorithm. The star tracker provides the best star position accuracy (random error: 9.0arcsec, and bias error: 0.74arcsec). The on-board attitude determination algorithm estimates attitude quaternion by applying an extended Kalman filter. The off-line attitude estimation introduced an extended-Kalman-filter-based smoother. To minimize the alignment change, the sensors are placed on the optical bench subject to precise temperature control. The jitter sensor provides precise angular information (0.010arcsec) from 2Hz to 500Hz and extends the attitude determination bandwidth. The dual-frequency GPS receiver capable of measuring pseudoranges and carrier phases allows the ground-based position determination with sub-meter accuracy.

Precision Attitude and Orbit Control System for the Advanced Land Observing Satellite

The Advanced Land Observing Satellite (ALOS) is a NASDA’s flagship for the high-resolution Earth observation. Characterized by simultaneous achievements of 2.5m resolution and global data collection, the ALOS mission requires a set of pointing requirements to provide precise geometric accuracy for observed images. In the pointing management framework designed to meet the pointing requirements, the Attitude and Orbit Control System (AOCS) imposes itself stringent requirements: attitude stability (3.9× 10−4deg p-p), attitude determination accuracy (onboard: 3.0 × 10−4deg), and position determination accuracy (off-line: 1m). A variety of solution approaches were developed and implemented for AOCS. This challenge includes precision star tracker, precision GPS receiver, high-performance onboard computer, star-sensor based attitude determination and control, phase stabilization of flexible structures, and precision cooperative control. Presented in this paper are the design and test results for the AOCS protoflight model, with an emphasis on the development of the new approaches enabling its precision.

Autonomous precision orbit control of ALOS-2 for repeat-pass SAR interferometry

ALOS-2, the next-generation Japanese SAR satellite, is designed to perform autonomous precise orbit control of Earth-referenced repeating orbits for effective repeat-pass SAR interferometry. The orbit control accuracy requirement of ALOS-2 is 500m (95%) with respect to the reference Earth-fixed flight path. This accuracy is guaranteed for all latitudes by not only drag-makeup maneuvers but also frequent inclination maneuvers. The on-board software of ALOS-2 can handle operations of orbit determination, maneuver prediction and planning, and maneuver executions for both drag-makeup maneuvers and inclination maneuvers. This feature of autonomy is expected to be great help for efficient ground operations of ALOS-2.

Accuracy assessment of ALOS optical instruments: PRISM and AVNIR-2

This paper describes the updated results of calibration and validation to assess the accuracies for optical instruments onboard the Advanced Land Observing Satellite (ALOS, nicknamed “Daichi”), which was successfully launched on January 24th, 2006 and it is continuously operating very well. ALOS has an L-band Synthetic Aperture Radar called PALSAR and two optical instruments i.e. the Panchromatic Remotesensing Instrument for Stereo Mapping (PRISM) and the Advanced Visible and Near Infrared Radiometer type-2 (AVNIR-2). PRISM consists of three radiometers and is used to derive a digital surface model (DSM) with high spatial resolution that is an objective of the ALOS mission. Therefore, geometric calibration is important in generating a precise DSM with stereo pair images of PRISM. AVNIR-2 has four radiometric bands from blue to near infrared and uses for regional environment and disaster monitoring etc. The radiometric calibration and image quality evaluation are also important for AVNIR-2 as well as PRISM. This paper describes updated results of geometric calibration including geolocation determination accuracy evaluations of PRISM and AVNIR-2, image quality evaluation of PRISM, and validation of generated PRISM DSM. These works will be done during the ALOS mission life as an operational calibration to keep absolute accuracies of the standard products.

Development of a New Generation Spaceborne GPS Receiver

We are investigating a New Generation Spaceborne GPS Receiver that can determine a position more precisely, but which is smaller, with lower cost and lower power consumption than a conventional receiver. This new type of spaceborne receiver includes a CMOS Silicon on Insulator (SOI) chip and adopts a direct