<commit_before>---
layout: post
title: Free Sources of SAR Data
description: "Sources and ways to work with a free SAR data."
modified: 2015-09-16
tags: [sar, geospatial, opensource, free, satellite]
image:
  -- feature: abstract-3.jpg
  creditlink: http://treuropa.com/technique/sar-imagery/
---

Free Synthetic Aperture Radar data can be some of the hardest to find, but it is out there if you look hard enough. These products are often provided in CEOS or other formats and there are a variety of tools available for working with the data.

## SAR satellites and orbital paths

The most common way to receive SAR data, is a sensor on a satellite. The family of satellites that have carried, are carrying, or will be carrying SAR sensors for commercial applications are presented below (_Figure 1_).

<figure>
	<img src="/images/posts/2015/09/16/sar-satellites.jpg" alt="SAR satelllites">
	<figcaption>Figure 1</figcaption>
</figure>

All satellites equipped with SAR sensors orbit the Earth on a near-polar orbit at an altitude ranging from 500 to 800km above the Earth’s surface, depending on the satellite platform hosting the SAR sensor. The time taken for a satellite to re-pass over the same area is called the ‘revisiting time’.

The angle between true north-south and the satellite orbit varies slightly, depending on the satellite, but in general lies in the range of 10 degrees. The circumpolar orbits of all SAR satellites mean that for half of their trajectory they are traveling from the north pole towards the south pole. This direction is referred to as a descending orbit. Conversely, when the satellite is traveling from the south pole towards the north pole, it is said to be in an ascending orbit (_Figure 2_).

<figure>
	<img src="/images/posts/2015/09/16/orbital-paths.jpg" alt="Orbital paths">
	<figcaption>Figure 2</figcaption>
</figure>

## Alaska Satellite Facility

This [university](https://www.asf.alaska.edu/) provides a wide amount of tools to work with SAR data. The most reasonable is an [API](https://www.asf.alaska.edu/data-tools/interactive-api-tool-accessing-sar-data/) which provides a possibility to query data from different sources. The API includes [search by products](https://vertex.daac.asf.alaska.edu/) data from these storages:

* A3
* AI
* AS
* E1
* E2
* J1
* R1
* UA
* [AIRMOSS](https://airmoss.jpl.nasa.gov/) -- North American SAR coverage (via plane). There are 2-3 campaigns per year (depending on the length of the site's growing season). During each site campaign, AirMOSS will collect data at least three times over a 10-15 day period to quantify evaporative and transpiration processes occurring at finer time scales over the study areas.
* [AIRSAR](http://airsar.jpl.nasa.gov/) -- contains a wide range of data, covering different parts of the Earth (via plane). The first mission started at 1990 year, and finished in 2003. So, the ASF API provides access to this historical data, which not updating.
* [ALOS](http://global.jaxa.jp/projects/sat/alos/) -- Japan satellite ALOS was launched in 2006. The satellite contained three sensors that were used for cartography and disaster monitoring of Asia and the Pacific (PRISM, AVNIR-2, PALSAR). In April 2011, the satellite was found to have switched itself into power-saving mode due to deterioration of its solar arrays. Its successor ([ALOS-2](http://www.jaxa.jp/projects/sat/alos2/index_j.html)) -- was successfully launched in 2014, ALOS-2/CIRC data available [here](http://circgs.tksc.jaxa.jp/data/index.html), all rasters has resolution up to 10m.
* [ERS (ERS-1, ERS-2)](https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/ers) -- ERS-1 and ERS–2, were launched into the same orbit in 1991 and 1995 respectively with spatial resolution 30m. Both satellite deorbited. The similar to these satellites ENVISAT finished mission in 2012, due to losing connection with it. 
* [JERS-1](https://directory.eoportal.org/web/eoportal/satellite-missions/j/jers-1) -- was launched in 1992 from Tanegashima Space Center, and deorbited in 1998 due to techincal problems, had 30m resolution.
* [RADARSAT-1](http://www.asc-csa.gc.ca/eng/satellites/radarsat1/) -- a Canadian satellite, now it is inactive
* [SEASAT](http://science.nasa.gov/missions/seasat-1/) -- Seasat was the first satellite designed for remote sensing of the Earth's oceans with synthetic aperture radar. Its mission started and finished in 1978.
* [UAVSAR](http://uavsar.jpl.nasa.gov/) -- Similar mission to AIRMOSS and AIRSAR.
* [SMAP](http://smap.jpl.nasa.gov/) (_not found in the official documentation_) -- is a new satellite with a low resolution (1km to 36km) 
* Also possible another _SAR platforms_, which listed nether here nor in the official documentation

This briefly analysis shows that ASF API provides very old, and hardly refreshable data. The description for some products was not found, but this data is rather old and can be used only for historical research.

## Epilogue

What is in the end? Why only ASF API observed? ASF API is a sort of SAR data sources aggregation. The only actual data (free and found in public sources during this small research) is provided by [ALOS-2](http://www.jaxa.jp/projects/sat/alos2/index_j.html) satellite, but, there are no sources (or were not found) providing the daily whole earth coverage. In conclusion, it is possible to add, that the SAR data is one of the hardest things to find, may be there are sources of commercial data, but it is a topic for antother post.<commit_msg>fix article<commit_after>---
layout: post
title: Free Sources of SAR Data
description: "Sources and ways to work with a free SAR data."
modified: 2015-09-16
tags: [sar, geospatial, opensource, free, satellite]
image:
  -- feature: abstract-3.jpg
  creditlink: http://treuropa.com/technique/sar-imagery/
---

Free Synthetic Aperture Radar data can be some of the hardest to find, but it is out there if you look hard enough. These products are often provided in CEOS or other formats and there are a variety of tools available for working with the data.

## SAR satellites and orbital paths

The most common way to receive SAR data, is a sensor on a satellite. The family of satellites that have carried, are carrying, or will be carrying SAR sensors for commercial applications are presented below (_Figure 1_).

<figure>
	<img src="/images/posts/2015/09/16/sar-satellites.jpg" alt="SAR satelllites">
	<figcaption>Figure 1</figcaption>
</figure>

All satellites equipped with SAR sensors orbit the Earth on a near-polar orbit at an altitude ranging from 500 to 800km above the Earth’s surface, depending on the satellite platform hosting the SAR sensor. The time taken for a satellite to re-pass over the same area is called the ‘revisiting time’.

The angle between true north-south and the satellite orbit varies slightly, depending on the satellite, but in general lies in the range of 10 degrees. The circumpolar orbits of all SAR satellites mean that for half of their trajectory they are traveling from the north pole towards the south pole. This direction is referred to as a descending orbit. Conversely, when the satellite is traveling from the south pole towards the north pole, it is said to be in an ascending orbit (_Figure 2_).

<figure>
	<img src="/images/posts/2015/09/16/orbital-paths.jpg" alt="Orbital paths">
	<figcaption>Figure 2</figcaption>
</figure>

## Alaska Satellite Facility

This [university](https://www.asf.alaska.edu/) provides a wide amount of tools to work with SAR data. The most reasonable is an [API](https://www.asf.alaska.edu/data-tools/interactive-api-tool-accessing-sar-data/) which provides a possibility to query data from different sources. The API includes [search by products](https://vertex.daac.asf.alaska.edu/) data from these storages:

* A3
* AI
* AS
* E1
* E2
* J1
* R1
* UA
* [AIRMOSS](https://airmoss.jpl.nasa.gov/) -- North American SAR coverage (via plane). There are 2-3 campaigns per year (depending on the length of the site's growing season). During each site campaign, AirMOSS will collect data at least three times over a 10-15 day period to quantify evaporative and transpiration processes occurring at finer time scales over the study areas.
* [AIRSAR](http://airsar.jpl.nasa.gov/) -- contains a wide range of data, covering different parts of the Earth (via plane). The first mission started at 1990 year, and finished in 2003. So, the ASF API provides access to this historical data, which not updating.
* [ALOS](http://global.jaxa.jp/projects/sat/alos/) -- Japan satellite ALOS was launched in 2006. The satellite contained three sensors that were used for cartography and disaster monitoring of Asia and the Pacific (PRISM, AVNIR-2, PALSAR). In April 2011, the satellite was found to have switched itself into power-saving mode due to deterioration of its solar arrays. Its successor ([ALOS-2](http://www.jaxa.jp/projects/sat/alos2/index_j.html)) -- was successfully launched in 2014, ALOS-2/CIRC data available [here](http://circgs.tksc.jaxa.jp/data/index.html), all rasters have resolution  2m - 10m.
* [ERS (ERS-1, ERS-2)](https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/ers) -- ERS-1 and ERS–2, were launched into the same orbit in 1991 and 1995 respectively with spatial resolution 30m. Both satellite deorbited. The similar to these satellites ENVISAT finished mission in 2012, due to losing connection with it. 
* [JERS-1](https://directory.eoportal.org/web/eoportal/satellite-missions/j/jers-1) -- was launched in 1992 from Tanegashima Space Center, and deorbited in 1998 due to techincal problems, had 30m resolution.
* [RADARSAT-1](http://www.asc-csa.gc.ca/eng/satellites/radarsat1/) -- a Canadian satellite, now it is inactive
* [SEASAT](http://science.nasa.gov/missions/seasat-1/) -- Seasat was the first satellite designed for remote sensing of the Earth's oceans with synthetic aperture radar. Its mission started and finished in 1978.
* [UAVSAR](http://uavsar.jpl.nasa.gov/) -- Similar mission to AIRMOSS and AIRSAR.
* [SMAP](http://smap.jpl.nasa.gov/) (_not found in the official documentation_) -- is a new satellite with a low resolution (1km to 36km) 
* Also possible another _SAR platforms_, which listed nether here nor in the official documentation

This briefly analysis shows that ASF API provides very old, and hardly refreshable data. The description for some products was not found, but this data is rather old and can be used only for historical research.

## Epilogue

What is in the end? Why only ASF API observed? ASF API is a sort of SAR data sources aggregation. The only actual data (free and found in public sources during this small research) is provided by [ALOS-2](http://www.jaxa.jp/projects/sat/alos2/index_j.html) satellite, but, there are no sources (or were not found) providing the daily whole earth coverage. In conclusion, it is possible to add, that the SAR data is one of the hardest things to find, may be there are sources of commercial data, but it is a topic for antother post.
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