[Qgis-user] Convert an ALOS PALSAR DEM from ellipsoidal to geoid.

[Fielding, Eric J (US 329A)]

Hello Eddison,

I am not sure what source you are using for the ALOS PALSAR DEM that you are describing. As far as I know, there is no systematically processed DEM made from ALOS PALSAR data. There is a DEM composite that the Alaska Satellite Facility (ASF) is using for their Radiometric Terrain Correction (RTC) processing of the ALOS PALSAR that they have resampled from other sources. See their web page for details:
https://asf.alaska.edu/data-sets/derived-data-sets/alos-palsar-rtc/alos-palsar-radiometric-terrain-correction/#dem_information

The web page explains that they were using the SRTM1 (1-arcsecond or about 30 m) DEM interpolated to the 12.5 meter spacing of the ALOS PALSAR RTC products. The SRTM DEM has the EGM96 geoid reference. I think they may recently have changed to using the Copernicus GLO-30 DEM that is also 1-arcsecond spacing but uses the EGM2008 geoid reference. Again, they will interpolate it to the 12.5 m spacing for their ALOS PALSAR RTC processing. Over the USA, they used the USGS NED DEMs that are higher resolution.

If this is the source of the “ALOS PALSAR DEM” that you are using, you will be better off getting the original DEM for your area from either the Copernicus GLO-30 DEM sources (there are several) or the USGS NED DEM sources. You will still have to do the geoid to ellipsoid height conversions but it won’t be modified by the interpolation that ASF is doing in their RTC processing.

++Eric Fielding
JPL

Message: 1
Date: Mon, 2 Jan 2023 20:08:39 -0600
From: Eddison Araya <eddisonjose at gmail.com>
To: Nicolas Cadieux <njacadieux.gitlab at gmail.com>
Cc: qgis-user <qgis-user at lists.osgeo.org>
Subject: Re: [Qgis-user] Convert an ALOS PALSAR DEM from ellipsoidal
        to geoid.
Message-ID:
        <CAC-LqC=PqEiqoi4D7eDh0t3JQtK8fepPLWXKkYyR4OfLdpNRaw at mail.gmail.com>
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Hello yes, thank you very much, according to that source it is EMG-2008

Regards!

eddison

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