# How to change polarization in CRTM?

**URL:** <https://forums.jcsda.org/t/how-to-change-polarization-in-crtm/295>\
**Category:** CRTM\
**Created:** [March 28, 2022, 4:03pm UTC](https://forums.jcsda.org/t/how-to-change-polarization-in-crtm/295 "2022-03-28T16:03:09Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Jun](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.jcsda.org/jun/32/122_2.png) [@Jun](https://forums.jcsda.org/u/Jun)\
**Post date:** [March 28, 2022, 4:03pm UTC](https://forums.jcsda.org/t/how-to-change-polarization-in-crtm/295/1 "2022-03-28T16:03:09Z")

</div>

Hi,  
In CRTM, if the sensor is fixed in the SensorData structure, the polarization of each channel is fixed. For example, the polarization of ATMS channel 1,2, and 16 is QV and the other channels are QH. Is it possible to calculate QH brightness temperature for channel 1, 2, and 16, QV brightness temperature for other channels through CRTM?  
Thanks!

Jun

---

<div class="post-metadata">

**Author:** ![StegmannJCSDA](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.jcsda.org/stegmannjcsda/32/53_2.png) [@StegmannJCSDA](https://forums.jcsda.org/u/StegmannJCSDA)\
**Post date:** [April 11, 2022, 7:49pm UTC](https://forums.jcsda.org/t/how-to-change-polarization-in-crtm/295/2 "2022-04-11T19:49:06Z")

</div>

@Jun the instrument polarization in the CRTM is supposed to be fixed.  
You can try the following workaround:

1. In your CRTM calculation, load the `SC` data:

```nohighlight
  ! ...Spectral coefficients
  USE CRTM_SpcCoeff , ONLY: SC

```

1. After the call to `CRTM_Init()`, modify the `SC` data with the polarization scheme you want:

```nohighlight
SC(1)%Polarization(begin_chan : end_chan) = desired_polarization_scheme

```

1. Run the CRTM calculation as usual.

This hasn’t been tested though.

---

<div class="post-metadata">

**Author:** ![Jun](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.jcsda.org/jun/32/122_2.png) [@Jun](https://forums.jcsda.org/u/Jun)\
**Post date:** [May 2, 2022, 2:55pm UTC](https://forums.jcsda.org/t/how-to-change-polarization-in-crtm/295/3 "2022-05-02T14:55:47Z")

</div>

I’ve tested this in my code:  
SC(1)%Polarization(1:2)=10  
SC(1)%Polarization(3:15)=9  
SC(1)%Polarization(16)=10  
SC(1)%Polarization(17:22)=9  
The output seems reasonable.  
Thanks a lot!

Jun

---

<div class="post-metadata">

**Author:** ![StegmannJCSDA](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.jcsda.org/stegmannjcsda/32/53_2.png) [@StegmannJCSDA](https://forums.jcsda.org/u/StegmannJCSDA)\
**Post date:** [May 11, 2022, 5:25pm UTC](https://forums.jcsda.org/t/how-to-change-polarization-in-crtm/295/4 "2022-05-11T17:25:16Z")

</div>

Thank you for confirming.