Phased Array L-band Synthetic Aperture Radar (PALSAR) data from Japan’s Advanced Land Observing Satellite (ALOS-1) mission are now unrestricted, and can be accessed by scientists and researchers around the world. These data are processed, archived, and distributed by the Alaska Satellite Facility Distributed Active Archive Center (ASF DAAC), which is part of the Alaska Satellite Facility (ASF) at the University of Alaska Fairbanks Geophysical Institute and is one of NASA's Earth Observing System Data and Information System (EOSDIS) DAACs.
While NASA has a “free and open” data policy, meaning that NASA does not charge for their data or impose restrictions on who can access data, these data use policies vary in other countries. Since ALOS-1 was a Japan Aerospace Exploration Agency (JAXA) mission, the Japanese government owns the data and required anyone wishing to use PALSAR data to first submit a proposal. Non-U.S. researchers also had to pay a fee for each scene they wanted.
Now that these data are unrestricted, anyone desiring access to these products only has to fill out a simple online registration. “This has a huge impact on the remote sensing community,” says Nettie La Belle-Hamer, Director of ASF. “Now the process for getting these data becomes much easier, and this makes these data available to a much broader international crowd than could access them before.”
The specific PALSAR data that are unrestricted are Level 1.0 (Unprocessed/Raw) and Level 1.5 (Geo-referenced Amplitude Image) data products along with Radiometrically Terrain Corrected (RTC) data products, all of which are available through ASF DAAC’s ALOS-1 PALSAR data page.
What makes synthetic aperture radar, or SAR, technology valuable for remote sensing is that it allows observations to be taken day or night, in almost any weather conditions. SAR bounces a microwave beam off the Earth’s surface, resulting in detailed images showing surface properties. PALSAR builds on the benefits of SAR by using a wavelength called L-band. L-band is extremely flexible, and provides information for a broad range of science disciplines. Some of the many applications of PALSAR data include tree species classification and forest canopy estimation, geologic structure interpretation, land surface and soil moisture analysis, topographical change detection, and oil slick assessment.
“It’s a true 24/7 data set,” says Franz Meyer, Chief Scientist for the ASF and Associate Professor in the Geophysical Institute. “It can observe the planet regularly no matter if it’s day or night, and no matter what the weather conditions are. This makes it very useful for analyzing changes over time. This has always been the advantage of PALSAR.”
For scientists, making these data unrestricted creates opportunities for new research. “Now, it is more likely that scientists who are not used to using SAR data are going to jump into this field and download these data sets, and analyze these data, and find interesting information in the data,” says Meyer.
The National Oceanic and Atmospheric Administration (NOAA) originally brought the ALOS-1 data to the U.S. as part of a partnership with JAXA to serve as their U.S. government partner, and ASF became an agent of NOAA for managing ALOS-1 data. NASA joined this team by providing Japan access to orbiting satellites to relay data from the ALOS-1 satellite to ground stations in the Western Hemisphere and then to the ASF for processing. The agreement between NASA, NOAA, and JAXA to use the NASA relay satellites in the ALOS-1 mission greatly increased the coverage and the amount of ALOS-1 data. “The use of the [NASA] relay satellites was a huge asset NASA brought to the table, and this was an important international achievement,” says La Belle-Hamer.
The mission of ASF is to make remote sensing data accessible, and it has three major components: a satellite tracking ground station, which is part of NASA’s worldwide Near Earth Network system of ground stations; the ASF Enterprise, which focuses on applications of remote-sensing data; and ASF DAAC, which is the NASA home of SAR data. The ASF DAAC specializes in collecting, processing, archiving, and distributing SAR data from a variety of satellite and airborne missions, and is one of one of the EOSDIS DAACs that process, archive, and distribute discipline-specific data as part of NASA’s Earth Science Data Systems (ESDS) Program.
High-level discussions to remove the restrictions to using ALOS-1 data have been conducted since the launch of the mission in 2006, and it was Japan’s decision to make PALSAR data (along with ALOS-1 data from the Advanced Visible and Near Infrared Radiometer type 2, or AVNIR-2, instrument) unrestricted.
La Belle-Hamer observes that ASF DAAC already has seen a noticeable increase in the volume of PALSAR data they are distributing, especially requests from foreign countries, and points out that this change gives the entire scientific community access to a huge amount of data they previously could not access. She also stresses that, in the big picture, having these data unrestricted fulfills higher values as well. “This is about research. This is about basic science,” she says. “This is what NASA does, and this is why we do what we do.”
Explore ASF DAAC PALSAR data through the ASF website.