4
$\begingroup$

I have been making RGB photos of AVHRR images from NOAA CLASS using the preview images (channel 2 & channel 4)As you can see, it isn't very good.

As you can see, it isn't very good. I have been wanting to use channel 1 and channel 3 images, but the only way to access such images is by ordering the images. I tried opening the images of inventory ID 0295859. When I ordered the images and download them, they have a file name of-

NSS.GHRR.NH.D89112.S0445.E0637.B0295859.WI

I tried opening the images, but nothing I did worked. I've tried extracting the files and attempted to open them using QGIS and ArcGIS, but nothing happened.

The image would look like this colorized: Example]

How do I open this file? If it helps, the image is from 1989.

Edit: Here's an updated version:

Improve this question
$\endgroup$
1
  • $\begingroup$ If you provide one of the files, I can improve my answer with imagery (sorry, I'm too lazy to go to NOAA CLASS right now). $\endgroup$
    – gerrit ♦
    Jan 5 at 11:55

3 Answers 3

Reset to default
6
$\begingroup$

You can use the Python library satpy to read AVHRR GAC data:

from satpy import Scene
sc = Scene(filenames=["NSS.GHRR.NJ.D95056.S1116.E1303.B0080506.GC"], reader=["avhrr_l1b_gaclac"])
sc.load(["1", "2", "4", "5", "cloudtop"])
ls = sc.resample("africa")
ls.save_datasets()

This will give you a GeoTIFF of the file resampled onto Africa, for channels 1, 2, 4, and 5. It will also give you an RGB Satpy calls "cloudtop", which is a combination of channels 3B, 4, and 5. It will look very different from the true color RGB in your image. You can load the GeoTIFF into standard GIS desktop software. You can also write a variety of other output formats. Check the Satpy documentation for details.

For a full list of RGBs that you can generate with Satpy for AVHRR data, call sc.available_composite_names() after you have created the Scene object. None of the RGBs will look quite like true color, but natural_color (if available) comes closest. The natural_color and cloudtop RGBs depend on the availability of channels 3A or 3B, which are satellite and solar zenith angle dependent.

There also exists a desktop tool called sift that can be used as a GUI to read any data Satpy can read, in case you are not comfortable with simple programming. Support for polar satellites such as AVHRR was recently added to SIFT.

Improve this answer
$\endgroup$
2
  • $\begingroup$ I tried this in VS Code but it said that satpy 'extension' isn't available. But I have it installed on my system. What do I do? $\endgroup$
    – Kamty
    Sep 24 at 4:52
  • $\begingroup$ @Kamty You probably didn't install it correctly. That's a Python programming/installation question and has nothing to do with satpy as such. $\endgroup$
    – gerrit ♦
    Sep 25 at 6:57
2
$\begingroup$

As you can see, it isn't very good.

From my perspective, it is very good. The raw data is AVHRR data scanned on a line-by-line and pixel-by-pixel sense. To make better sense of that data you might want to map the data to a grid. There are many people who want the raw data.

Improve this answer
$\endgroup$
2
$\begingroup$

AVHRR does not capture green or blue so making an RGB image is not possible. Your colorized example looks like a false-color representation of AVHRR NDVI images using a green to purple color band to me. Migrate your question over to Geographic Information Systems Stack Exchange for help with QGIS and ArcGIS. Best to make your data available for download if possible.

Improve this answer
$\endgroup$
1
  • 1
    $\begingroup$ AVHRR does not capture green or blue so making an RGB image is not possible — that isn't accurate. Making a true color RGB image is not possible, but false colour combinations very much are possible. $\endgroup$
    – gerrit ♦
    Jan 5 at 11:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.