Hyper-spectral geotiff support in snap

ghansham · October 19, 2019, 12:52pm

Dear Sir

I want to know what metadata needs to be put along with geotiff to get spectral view working in snap.
And I have CF compliant netcdf files. But as CF conventions are quite young as far as hyperspectal data is concerned. What metadata should be put in the netcdf-4 file to get spectral viewer working.

regards
Ghansham

marpet · October 21, 2019, 7:38am

For Geotiff this is currently not possible. The geotiff format does not define a standard for wavelength.

For NetCDF, you can add the attribute “radiation_wavelength” to a variable.
You can also specify the unit. Use “radiation_wavelength_unit” as attribute name. If you choose other then ‘nm’, then the value of radiation_wavelength will be converted to ‘nm’ to fit to SNAP expectation.

ghansham · October 21, 2019, 2:39pm

Is it possible for you to share sample ncml of the Hyperspectral netcdf? Also can you point which module is handling this as far as data source is concerned? And does this mean, we need to store data in separate variables corresponding to each wavelength. I thought we could store single 3d variable with coordinates set to band, lat, lon. And band is a coordinate variable with standard_name attribute set to “sensor_band_central_radiation_wavelength” and units set and values of central wavelengths. See the url below, it talks about cf conventions for spectral coordinates.

github.com

Unidata/EC-netCDF-CF/blob/master/swath/swath.adoc

= Encoding of Swath Data in the Climate and Forecast Convention
Aleksandar Jelenak; David Santek; Kent Yang; Robert Carp
:toc: preamble
:toclevels: 4
:sectnums:
:icons: font
:linkattrs:
:imagesdir: figures/

====
Proposal status: *[red]#FINAL DRAFT/2018-06-19#*.
====

// Example counter
:example-count: 0

== Introduction

This is a proposal for an extension of the http://cfconventions.org[Climate and Forecast metadata convention^] (CF) to standardize the encodings of Earth Science swath data in the original instrument viewing geometry. The aim is to have some form of this document added to a future version of the CF convention. The proposal is based on the CF http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/cf-conventions.html[version 1.7^] although backward compatibility is not necessarily an objective.

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Looking forward to listen from you.
Also please mention where the data source for netcdf and cf-netcdf is being handled within snap.

Regards
Ghansham