ALOS 1/2 Issues

Goals

• Solve existing problems in SNAP to facilitate the use of ALOS-1 and 2 products.

Background and strategic fit

ALOS products are poorly supported in SNAP. There are differences in files obtained from different sources, some products are reported as causing errors when importing, there are difficulties orthorectifying, general issues with L1.5 data and georeferencing, and issues with coregistration.

Assumptions

Requirements

User interaction and design

Questions

Below is a list of questions to be addressed as a result of this requirements document:

Comments

Information about the ALOS 2 products, as well as issues reported on the forum with ALOS 1 and 2 data:

• Overview

• Format

  • CEOS SAR Product Format Description

  • GeoTiff Product Format Description

• Data

  • ALOS 1 data is available through ASF Vertex

  • ALOS 2

    • Sample data

    • Simulated Sample Data

    • Level 2.2 ScanSAR is available on Google Earth Engine (account needed)

    • ScanSAR that is “freely available” is described here as being available only through Google Earth Engine and the JAXA G-Portal, which links to the download site that refuses to load, so as of now, Earth Engine is the only option. Explanation of the situation here.

• Issues

  • Common documented issues:

    • ALOS Orthorectification (seems solved, https://forum.step.esa.int/t/alos1-geocoding-and-terrain-correction-problem-in-s1/1488 ). Often talks about products being terrain corrected to the wrong spot

    • Terrain Correction on level 1.5 ALOS 2 products (potential solution) Level 1.5 data is geocoded but not georeferenced and SNAP run into problems with this, so the solution is SAR mosaic with just one file. Geocoding seems to be inaccurate in some cases (ALOS2 data downloaded from JAXA, rather than ASF). Other report of problems with geocoding of L1.5

    • NullPointerException when importing https://forum.step.esa.int/t/alos-2-l1-5-geotiff-not-opening/30147 https://forum.step.esa.int/t/error-import-alos-2/35671 (comment describing workaround)

    • Problems creating interferograms with ALOS data, potentially caused by issues with coregistration. Report of problems with coregistration. More problems

    • ALOS2 data seems to generally fail to line up properly with other products, at least sometimes

    • There is a difference between data downloaded from ASF Vertex and data downloaded directly from JAXA. Data from ESA matches one but I am unsure which, and I don’t exactly know what the difference is. (Example, ALOS1 downloaded from ASF works with ellipsoid correction, but from ESA it fails)

• Some issues for which the solution or group they belong to is unclear

  • (problems with ramps on interferograms)

• Current ALOS tutorials

  • http://step.esa.int/docs/tutorials/ALOS PALSAR Orthorectification Tutorial.pdf

Not Doing