--Harry Stern (harry@apl.washington.edu), Polar Science Center, Seattle, WA
The Alaska Synthetic Aperture Radar (SAR) Facility (ASF) held the first meeting of its new ASF User Working Group (ASFUWG) on May 18-19 in Fairbanks. The 26 people in the ASF group are mostly SAR data users from the research and operational communities, representing a wide range of disciplines and institutions. Members also include experts on data systems and imaging radars, as well as the Chief Scientist of ASF (Verne Kaupp), the head of ASF Development at the Jet Propulsion Laboratory (David Nichols), and NASA's ASF Program Scientist (Prasad Gogineni), who is also the manager of NASA's Polar Research Program.
The purpose of this DAAC advisory group is to make recommendations to ASF and NASA in order to improve the products and services at ASF, and to ensure that the U.S. research and operational communities continue to have timely access to SAR data collected around the world by current and future spaceborne SARs. Toward this end, the most important result to come out of the meeting was the recommendation that NASA negotiate agreements with the European, Canadian, and Japanese space agencies for reception (at ASF) and access (worldwide) to SAR data from the instruments that those nations plan to put in orbit within the next five years. This recommendation is in the form of a 46-page white paper entitled "The Critical Role of SAR in Earth System Science," written by the ASFUWG in the weeks following the meeting. The paper is available on the ASFUWG web site at http://psc.apl.washington.edu/ASFUWG.
Many other important issues were discussed at the meeting. After a brief introduction to ASF and future SAR missions, the main topics from the meeting and the next ASF Science Plan are described below.
ASF is unique among NASA's DAACs in operating a ground receiving station as well as processing, archiving, and distributing the data it collects. In addition, SAR data acquired at McMurdo (Antarctica) and foreign ground stations are sent to ASF for processing. The four satellites that currently carry SARs are operated by foreign flight agencies: ERS-1 and ERS-2 (European), JERS-1 (Japanese), and Radarsat-1 (Canadian). This presents unique challenges for ASF in terms of scheduling and acquiring the SAR data requested by U.S. users. For example, for Radarsat-1 there is a strict limit on the number of minutes per 24-day cycle allocated to U.S. users without cost. Also, SAR data that are downlinked at foreign ground stations are not immediately accessible through the EOSDIS interface. These data must first be shipped to ASF and "scanned" or cataloged there.
Several new satellites carrying SARs are scheduled for launch in the next five years: the European ENVISAT-1 (2000), the Canadian Radarsat-2 (2001), the U.S. LightSAR (2002), and the Japanese ALOS (2003). While the European, Canadian, and Japanese missions may be thought of as continuations of the current generation of SARs, they all add important new capabilities: ENVISAT-1 Advanced SAR (ASAR) has a ScanSAR mode and dual polarization; Radarsat-2 has a ScanSAR mode like its predecessor and full quadrature polarization; LightSAR is fully polarimetric and is designed with interferometric applications in mind; ALOS has a ScanSAR mode, dual polarization, and is particularly well designed for land-cover mapping. U.S. scientists and operational agencies will benefit greatly from this next generation of advanced SARs.
After welcoming remarks by the Chancellor of the University of Alaska Fairbanks and the Director of the Geophysical Institute, the acting director of ASF (Craig Lingle) gave an overview of recent scientific results accomplished with ASF data, and reported that ASF production levels are rising.
Prasad Gogineni reviewed the four major projects supported by data from ASF: The Radarsat Geophysical Processor System (RGPS), the Radarsat Antarctic Mapping Program (RAMP), boreal forest mapping, and Amazon forest mapping. In addition to these projects there are 61 investigations selected through NASA Research Announcements and 91 other investigations that use data from ASF. The use of SAR interferometry for applications ranging from ice-sheet dynamics to topographic mapping is contributing to the increase in the number of SAR data users.
Members of the ASFUWG each gave five-minute presentations to introduce themselves and their research to the rest of the group.
Verne Kaupp discussed the functions he believes the ASFUWG should undertake: assess the current state of ASF; identify and prioritize issues of concern to users; draft a five-year science plan for ASF; and advocate new mission support, as addressed by the white paper referenced above.
Jim Conner (ASF User Services) and Greta Reynolds (ASF Mission Planner) talked about the SAR data that have been acquired at foreign ground stations by user request through ASF, and gave a behind-the-scenes look at the procedures and flow of information, starting from the data acquisition request (DAR) and continuing through scheduling and acquisition to final cataloging. Because of the complications arising from the interactions with foreign stations and agencies, there is no automated order-tracking system in place by which users can keep track of the status of their orders. This is an area of concern that is being addressed.
The day concluded with a general discussion period. Members outlined the white paper mentioned above and made writing assignments.
Verne Kaupp and others reviewed the different projects and categories of SAR data users.
A new satellite receiving station on Svalbard is planned for the reception of EOS AM-1 data. This station could be made compatible for SAR data as well, which would improve Arctic coverage. The ASFUWG will recommend that NASA work out an agreement with the Canadian Space Agency (CSA) for the reception of SAR data at the Svalbard station.
Jason Williams (ASF calibration engineer) talked about the calibration and validation of SAR data. The many beam modes of Radarsat-1 make this a challenging task. The standard beams have been calibrated and the ScanSAR Wide Beam (SWB) mode will be done soon.
There were two "allocation" discussions. One involved the allocation of processing resources among the different projects listed above. The ASFUWG needs to assist ASF in assigning priorities and assessing the need for increased processing capacity. The second discussion focused on the 1519 minutes per 24-day cycle of Radarsat-1 that are allocated to U.S. users. When the total user requests exceed 1519 minutes, ASF must decide how to trim the requests to bring them within the allocation. Also, submitted requests are sometimes rejected by CSA due to scheduling conflicts, but there is usually not enough time to re-submit a modified request. This results in unused allocation time.
Rick Guritz (ASF Science Division) informed the group about software "tools" development at ASF. This includes programs for reading, mosaicing, and geocoding images, as well as more-advanced functions such as terrain correction. The ASFUWG was asked to recommend or prioritize the development of further software tools.
Tom Bicknell and Dave Cuddy (ASF Development at JPL) talked about the upcoming migration of all the SAR signal data to a Level-0 archive. This will preserve the data in a more-usable format and facilitate tape handling and maintenance. It also presents the opportunity to extract certain information from the signal tapes as they are scanned. For example, a browse archive could be created. The ASFUWG should consider the benefits and costs of such opportunities.
The last ASF Science Plan was written in 1989 in anticipation of the launches of ERS-1, JERS-1, and Radarsat-1. Now is the time to draft a new five-year science plan to guide SAR research through the next generation of advanced SARs onboard ENVISAT-1, Radarsat-2, LightSAR, and ALOS. Input is needed from a wide range of researchers and operational users regarding their anticipated or potential applications, and their required (or desired) SAR coverage in space and time. Groups or individuals interested in contributing to the science plan should contact Harry Stern (harry@apl.washington.edu) or Leslie Morrissey (lmorriss@nature.snr.uvm. edu), co-chairpersons of the ASFUWG. We plan to have a rough draft by the time of the next meeting, tentatively scheduled for the end of September in Seattle.
For more information on ASF, visit their web site at http://www.asf.alaska.edu. For more information on the ASFUWG, including minutes of the meeting, recommendations, the white paper, and e-mail addresses of members, visit the web site at http://psc.apl.washington.edu/ASFUWG.