Earthdata Forum

Dear EARTHDATA team:

I some days ago downloaded the following ASTER dataset of a location in my country (Peru) to do some geological mapping for a research project, using public domain GIS software (QGIS):

1) AST_05 (TIR emissivity, april 2006, see attachment)
2) AST_07XT (VIS and SWIR reflectivity, same location and date)

Unfortunately, I could not find the metadata in the downloaded folder.
I repeated the search after the notice of the ASTER dataset update posted today in this forum, but found the same problem: I could not find the metadata in the list of documents to be downloaded (see attached screenshot in PDF format I see in the Earthdata webpage).

In particular, I need the parameters to convert the imagery from DN (Digital Number) to meaningful physical values of emissivity and reflectance (a decimal and dimensionless number between 0 and 1). Please tell me how to download the metadata and what formula to use to convert the DN to meaningful physical values (between 0 and 1).

I guess it is something similar to this one (taken from the ESA's COPERNICUS SENTINEL-2 website)

physical_value_band_i = (DN_value_band_i + offset_band_i)*coefficient_band_i

Thank you in advance, and Happy New Year 2026!

@alberto_silva_2024 Thank you for your question. ASTER Version 3 data were decommissioned on Dec 15, 2025, and they are no longer available. ASTER V004 which is archived in CMR does not provide it as a separate file. So rather than being processed on demand the data will be archived in the cloud.

ASTER V4 Product User Guide: https://lpdaac.usgs.gov/documents/2265/ASTER_User_Guide_V4_pcP80n5.pdf

Below are three news items we recently released:
ASTER On-Demand Processing To End Dec. 15, 2025 | NASA Earthdata
ASTER Version 3 and 3.1 Data Products Decommissioned | NASA Earthdata
ASTER Version 4 Data Product Suite Released | NASA Earthdata

We have passed your concerns to our LP DAAC science team for some additional guidance. Once I hear back from them, I will follow up with you.
Kind regards,
Janice

@alberto_silva_2024 Please find the guidance our scientists provided.
Level-2 products are already in physical units. All you need to do is take the pixel value and multiply it by the scale factor to get the physical measurement.
Let me know if this helps.
LP DAAC User Services

Dear EarthData LP DAAC team:

Thank you for your answer, but please I need some additional information (or confirmation) about the following:

1) You said "Level-2 products are already in physical units. All you need to do is take the pixel value and multiply it by the scale factor".

This means that I just have to multiply the DN value by a constant coefficient=0.001, regardless of the allowed DN range (i.e for VNIR/SWIR= 0-to-1000 or for TIR = 0-to-65535)?

2) Where do I find the metadata in the version 4 COG file? I dowloaded it last week (29 december to be exact) but I could not find it in the downloaded folder, and have no clue where to find it. In the v4 guide (november 2025) says it should be in the COG file, but I did not see it (see screenshot of my folder).

3) After opening the file in QGIS I found an image in 16-bit format (that is, a raster image with a range per pixel of DN = [0; 2^16 -1] = [0; 65535]. In the image there were two bands (see QGIS screenshots):
3.1) The main band (with the ASTER data) with a somewhat reduced range (between DN= 0 and roughly DN=1000 aprox.)
3.2) A second band (called "alpha", no idea what it contains but is black in appearance, with some pixels at 0 and others at the maximum value allowed, and nothing in between...)
Now I ask: what information is in the "alpha-band" and how to use it, if at all?
Thank you again, and have a nice 2026!

@alberto_silva_2024 We have forwarded your questions to the science team to provide some additional assistance with your inquiry. I will follow up with you once I hear back from the science team.
Thank you for your patience.
Janice

@alberto_silva_2024 To better assist you can you provide the granule ID.

The granule IDs are (the location is in South-West Peru, Arequipa Region and are old images from 2006, before the 2008 SWIR sensor failure.

AST_05_00404292006151032_20250527002024 (for surface TIR emissivity)
AST_07XT_00404292006151032_20250527005505 (for surface VNIR/SWIR reflectivity)

See also the screenshots from the Earthdata portal (dated 30/12/2025).
I hope those IDs are enough. Thank you again.

@alberto_silva_2024 Please find the ASTER scientist further guidance to your questions.

Thank you for providing the granule ID. To further address your questions:

The ASTER 05 Emissivity Product is distributed as an unscaled uint16 product. To calculate the emissivity per pixel (range 0–1), you need to apply a scale factor of 0.001, as specified on the product page (https://cmr.earthdata.nasa.gov/search/concepts/V3489800782-LPCLOUD.html). You can use your GIS Band Math function to perform this scaling.
In this example, I scaled Band 10 and plotted the histogram.
Regarding the Alpha band in your example:
• Band 1 contains the emissivity data.
• Band 2 is the Alpha band.
It appears that QIS interprets the masking applied to fill invalid pixels in the product as a second (alpha) band when converting products from HDF to Cloud Optimized GeoTIFF. This is also the case for the ASTER 07XT product, where:
• Band 1 = Crosstalk Corrected Surface Reflectance
• Band 2 = Alpha band
If you are only interested in emissivity and Crosstalk Corrected Surface Reflectance values, the Alpha band can be ignored. Like the emissivity product, the ASTER 07XT product also requires the scale factor of 0.001 to be applied.
Finally, the .met file metadata was part of the previous on-demand architecture for version 3. Now that the products are archived, the metadata file has been updated to the ummg.json format.
To retrieve the umm-g.json file from the EarthData Search Client:
1. Click the three dots on the right side of the granule.
2. Select View details.
3. Click the Metadata tab.
4. Right-click the umm-g link and select Save link as to save the file locally.
Alternatively, you can click on umm-g to view the umm-g.json file in your browser.
I hope this helps. If you have further questions, please let us know.
LP DAAC User Services