Hiroko Imai

Improvement of AVNIR-2 Radiometric Calibration by Comparison of Cross-Calibration and Onboard Lamp Calibration

The Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) on-orbit radiometric performance has been improved through the comparison of cross-calibration and onboard lamp calibration. We proposed a new cross-calibration scheme which uses top-of-atmosphere reflectance functions of satellite zenith angle at temporally and spatially stable ground sites. Each function is made from Moderate Resolution Imaging Spectroradiometer (MODIS) 500-m resolution data over 16 days, which includes AVNIR-2 observation dates. The results showed that the radiances of AVNIR-2 bands 1 (463 nm), 2 (560 nm), and 3 (652 nm) agreed with the radiances of Aqua and Terra MODIS within 3% accuracy (standard deviation of 2%). AVNIR-2 band 4 (821 nm) had a difference of about 7% (AVNIR-2< MODIS) due to water-vapor absorption which could explain more than half of the 7%. Using many samples from this scheme, we found dependences of radiometric calibration errors within the field of view (FOV) and for different gain modes. The lamp calibration system onboard AVNIR-2 unveiled these dependences over the FOV and time. Furthermore, for the gain mode, consistent results could be retrieved using the cross-calibration scheme. The retrieved radiometric correction factors (over the FOV and gain modes) have been applied to the Japan Aerospace Exploration Agency AVNIR-2 processing scheme. The subsequent validation of the correction showed, for polar snow areas, an improved radiometric performance over the entire FOV.

Overview of ALOS-2 and ALOS-3

ALOS-2 and ALOS-3 will succeed to radar and optical mission of Advanced Land Observing Satellite “Daichi” which had contributed to cartography, regional observation, disaster monitoring, and resources surveys for more than 5 years until its termination of operation in May 2011. ALOS-2 carries the state-of-the-art L-band Synthetic Aperture Radar (SAR) called PALSAR-2 which succeeds to the ALOS/PALSAR with enhanced performance in both high resolution (1m * 3m at finest in the Spotlight mode) and wide swath (up to 490km in the ScanSAR wide mode). Wider bandwidth and shorter revisit time will give better conference for INSAR data analysis such as crustal deformation and deforestation. The Proto Flight Model of ALOS-2 including PALSAR-2 is under integration and testing at JAXA’s Tsukuba Space Center. ALOS-3 carries the optical sensor called PRISM-2 which succeeds to the ALOS/PRISM mission with enhanced performance in high resolution (0.8 m), wide swath (50 km) and high geo-location accuracy. PRISM-2 will acquire stereo pair images with two telescopes for stereo mapping and precise Digital Surface Models. It is also considered to carry Hyper-spectral Imager Suite (HISUI), which is developed by the Ministry of Economy, Trade and Industry (METI) of Japan. JAXA has conducted the phase-A study on ALOS-3 spacecraft and mission instruments, with prototype testing of key components. This paper describes an overview of ALOS-2 and ALOS-3.

Improvement of AVNIR-2 Radiometric Calibration by TOA Directional-Reflectance Cross-Calibration and On-Board Calibration Data

A cross-calibration scheme which uses top-of-atmosphere (TOA) reflectance functions of satellite zenith angle at temporally and spatially stable ground sites is proposed. Each function is made from MODIS 500m-channel observations over 16 days which includes AVNIR-2 observation dates. The results showed that radiances of AVNIR-2 channels 1 (463 nm), 2 (560 nm), and 3 (652 nm) agreed to the radiances of Aqua and Terra MODIS channels 3 (466 nm), 4 (554 nm) and 1 (646 nm) respectively within 5% accuracy. AVNIR-2 channel-4 (821 nm) decreased more than 5% by water-vapor absorption in some cases. Using many samples from this scheme, we found possible gain dependencies on Field Of View (FOV) and gain-modes. Lamp calibration system onboard AVNIR-2 showed dependencies on FOV, time change of the FOV error, and gain-mode consistent with the cross-calibration results. After correction of the identified errors, inter-channel consistency of FOV in the polar-snow scenes was improved.

A conceptual design of PRISM-2 for Advanced Land Observing Satellite-3 (ALOS-3)

The Japan Aerospace Exploration Agency (JAXA) is planning a satellite system including Advanced Land Observing Satellites 2 and 3 (ALOS-2 and ALOS-3) for the ALOS follow-on program. ALOS-3 will carry the optical sensor named “PRISM-2” and extend the capabilities of earlier ALOS missions. PRISM-2 will be able to collect high-resolution (0.8m) and wide-swath (50 km) imagery with high geo-location accuracy, as well as provide precise digital surface models (DSMs) using stereo pair images acquired by two telescopes. These capabilities are ideal for obtaining large-scale geographical information such as elevation and land cover-maps for use in many research areas and practical applications, including disaster management support. JAXA has conducted a phase A study of the ALOS-3 spacecraft and PRISM-2, and is now working on prototype models of key components of PRISM-2’s telescope, focal plane, and data compressor. This paper introduces a conceptual design for PRISM-2 and the ALOS-3 system.

Wide swath and high resolution stereo mapping by PRISM-2 onboard ALOS-3

Panchromatic Remote-sensing Instrument for Stereo Mapping 2 (PRISM-2), which will be used for the next high spatial resolution global land observation mission, will extend the capabilities of earlier Advanced Land Observing Satellite (ALOS) missions. PRISM-2 will be able to collect wide-swath (50 km) and high-resolution (0.8 m) images with high geo-location accuracy without ground control points. It will acquire stereo pair images from two telescopes for stereo mapping and precise Digital Surface Models (DSMs). This paper introduces the mission requirement for the next high spatial resolution global land observation mission and a conceptual design for PRISM-2.

Development and observation results of the Earth observation system for stratospheric platform

Earth observation from the Stratospheric Platform (SPF) has several advantages over traditional airborne or spaceborne observations. Primarily, SPF can continuously monitor a specific area with higher spatial resolution over a longer period of time. We have developed the Earth Observation System for SPF-II (EOSS) for examining the feasibility of observation missions from the SPF and for demonstrating some sensor technologies. EOSS consists of three sensors: Wide-Angle Multi-band Sensor - Visible and Near-Infrared (WAMS-VNIR) for observation of vegetation and aerosol; Wide-Angle Multi-band Sensor - Thermal Infrared (WAMS-TIR) for monitoring distribution and time variation of land surface temperature; and High Resolution Sensor (HRS) for traffic observation. Observation mission tests were performed in October and November 2004. This paper describes the development of the sensor instruments and the results of SPF-IIs Earth-observation mission.