<p>Unfortunately it's common for satellite data services to show these types of images qualitatively, omitting the units or even a colorbar.</p>
<p>This is an infrared image from the 10.8 micron channel (TIR1) of INSAT-3D.  That website you link to is a bit misleading because (for me at least) following the link puts the text describing the 0.65 micron visible channel under the image.  If you click &quot;Infrared&quot; in the sidebar of that page the text is replaced with the correct text about the 10.8 micron channel.</p>
<p>Given that TIR1 records are stored as 10-bit values (i.e., in the range 0 to 1023) and the color scale maxes out at 939, I suspect that they are just plotting the raw count data.  This is normally transformed into radiances by applying a linear scale and offset to put the data in physical units.</p>
<p>I had a quick look at the equivalent 10.8 micron image from Meteosat over the Indian Ocean (see below) and I get a similar count range and a similar image when I apply their color scale.  I also suspect that they've inverted their data, e.g., plotted <code>count_inv = 1024 - count</code>, to fit with the viewers' expectation that cold clouds appear white.</p>
<p><a href="https://i.sstatic.net/YemYG.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/YemYG.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2020-06-22T17:26:23.460Z
2020-06-22T17:26:23.460Z
Deditos
<p>I came across an infrared weather map like this
<a href="https://i.sstatic.net/oAS7I.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/oAS7I.jpg" alt="enter image description here" /></a></p>
<p>I couldn't find any legend on the colorbar's color convention. Initially, I thought that might be the
color for reflected light's wavelength, but there was no way to find out.
This image is obtained from <a href="https://mausam.imd.gov.in/imd_latest/contents/satellite.php#" rel="nofollow noreferrer">https://mausam.imd.gov.in/imd_latest/contents/satellite.php#</a>.</p>

CC BY-SA 4.0
2020-06-21T09:52:27.940Z
@a_donda I missed the text. The units are not clear to me. The values tell me that they are not temperature units. Can you shed some light on the quantity in the colorbar?
Galilean
<meteorology><weather-satellites>
Understanding the color coding of a weather map
Galilean
# Understanding the color coding of a weather map

(Asked by: username_0 on 2020-06-21)

I came across an infrared weather map like this
[![enter image description here](https://i.sstatic.net/oAS7I.jpg)](https://i.sstatic.net/oAS7I.jpg)

I couldn't find any legend on the colorbar's color convention. Initially, I thought that might be the
color for reflected light's wavelength, but there was no way to find out.
This image is obtained from <https://mausam.imd.gov.in/imd_latest/contents/satellite.php#>.

**Tags:** meteorology, weather-satellites

> **Comments:**
> **username_0**: @a_donda I missed the text. The units are not clear to me. The values tell me that they are not temperature units. Can you shed some light on the quantity in the colorbar?  

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## 1 answers

### Answer by username_1 on 2020-06-22. Score: 2 | Accepted answer

Unfortunately it's common for satellite data services to show these types of images qualitatively, omitting the units or even a colorbar.

This is an infrared image from the 10.8 micron channel (TIR1) of INSAT-3D. That website you link to is a bit misleading because (for me at least) following the link puts the text describing the 0.65 micron visible channel under the image. If you click "Infrared" in the sidebar of that page the text is replaced with the correct text about the 10.8 micron channel.

Given that TIR1 records are stored as 10-bit values (i.e., in the range 0 to 1023) and the color scale maxes out at 939, I suspect that they are just plotting the raw count data. This is normally transformed into radiances by applying a linear scale and offset to put the data in physical units.

I had a quick look at the equivalent 10.8 micron image from Meteosat over the Indian Ocean (see below) and I get a similar count range and a similar image when I apply their color scale. I also suspect that they've inverted their data, e.g., plotted `count_inv = 1024 - count`, to fit with the viewers' expectation that cold clouds appear white.

[![enter image description here](https://i.sstatic.net/YemYG.png)](https://i.sstatic.net/YemYG.png)


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