The Rising SAR of ALOS

by Larry Ledlow

Japan's Aerospace Exploration Agency (JAXA) plans to loft a new L-band SAR when their Advanced Land Observing Satellite (ALOS) takes flight next September. The Phase Array type L-band Synthetic Apeture Radar (PALSAR) will complement two optical instruments also aboard the four metric ton spacecraft. Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) is a four-band imager with a resolution of ten meters across a 70 km swath. While its predecessor flew aboard ADEOS, this instrument incorporates improved electronics and functionality like +/- 44 degrees cross-track steering

The Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) is a 2.5-meter spatial resolution. Its data will be used for extracting highly accurate digital elevation models (DEM). The PRISM has three independent optical systems for nadir, forward and backward looking to achieve along-track stereoscopy. Each telescope consists of several CCD detectors for pushbroom scanning. The nadir-looking telescope provides 70km width coverage; forward and backward telescope provide 35km width coverage each.

The real star in the ALOS line up is PALSAR, an active microwave sensor using L-band frequency for cloud-free and day-and-night observation. On-orbit and operational in the 2004-05 period, PALSAR will also provide an important complement to existing and planned C- and X-band SAR sensors. This instrument will offer more modes and higher performance than the JERS-1's SAR. PALSAR is capable of beam steering, full polarimetry, and ScanSAR. The fine resolution mode is a conventional one. The PALSAR will have another attractive observation mode, the ScanSAR mode, which will allow us to acquire a 250 to 350 km width (depending on the number of scans) of SAR images at the expense of spatial resolution. This is a three to five times wider swath than conventional SAR images. The development of the PALSAR has been a joint project between JAXA and Japan Resources Observation System Organization (JAROS).

All of this is good news for ASF users. Just over one year ago, ASF and NOAA formalized an agreement to operate Americas ALOS Data Node (AADN) in Fairbanks as part of JAXA's data distribution scheme. All orders for ALOS optical and SAR data from customers in the Americas will pass to ASF, either directly or through one of our AADN partners. ALOS metadata will be widely distributed, thus making selection and ordering greatly simplified for many users. Moreover, ALOS avoids restricted distribution lists seen in the past, and ASF intends to promoted all data sets widely in the research and public service communities. Initially available in ASF's mask only, near-real-time downlink services may be extended throughout North, Central, and South America.

The first two cycles (three months) are dedicated for global coverage by Fine-Beam, Single Polarization (FBS) HH 34.3 degree to obtain baseline data. After that, the PALSAR basic observation plan is as follows:

Ascending observations are nominal: with one global coverage per year by FBS HH 34.3 deg and two successive cycles' observations per year by Fine-Bean, Dual-Polarization (FBD) HH+HV 34.3

Descending observations are limited for: one global coverage per year by Wide Beam Mode 1 (WB1): ScanSAR 120 Mbps 5-scan and limited FBS, FBD, and WB1 over selected regions

These observation plans for PALSAR aim to satisfy three main themes: a) Mapping of terrestrial carbon sources and sinks, and changes therein (Kyoto & Carbon Initiative); b) SAR interferometery for Ortho rectification and DEM generalization and c) Monitoring of crustal movements Interferometric SAR (InSAR).

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