<p>For validation of model data, I want to compare the ozone data from model to the satellite results downloaded from the <a href="https://avdc.gsfc.nasa.gov/pub/data/satellite/Aura/OMI/V03/L2/OMPROFOZ" rel="nofollow noreferrer">following link</a>:</p>
<p>The satellite data are in DU(Dobson Unit) while the model data are in ppbv. To make them comparable, I converted the units of satellite data from DU to ppbv from the formula specified in the README file.</p>
<p><a href="https://i.sstatic.net/Pxkak.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Pxkak.png" alt="formula for conversion" /></a></p>
<p>But I have problem converting values of average kernel(AKs). The readme file specifies that</p>
<blockquote>
<p>Note the AKs for different units (e.g., DU or ppbv) are different, the DU/DU does not cancel out because the conversion from DU to ppbv varies with altitude (e.g. resulting from different T, P).</p>
</blockquote>
<p>But, I am not sure what is the right way convert the values of Average Kernel from DU/DU to ppbv/ppbv so that I can use its values.</p>

CC BY-SA 4.0
2022-02-15T00:31:06.690Z
potentially related [Dobson unit](https://en.wikipedia.org/wiki/Dobson_unit)
uhoh
CC BY-SA 4.0
2022-02-15T02:32:02.143Z
If I understand your question, the averaging kernels aren't part of the conversion which is correct.  Instead, the averaging kernel is a unitless multiplier (should be near 1.0) that is applied at every layer.  You don't convert units of the AK because by definition it is unitless.  You can do the conversion without the AKs, and compare the biases with/without (as discussed in the link you provided).
f.thorpe
CC BY-SA 4.0
2022-02-15T02:37:21.587Z
Also see Figure 1 for an example of averaging kernels and how they are centered on 1.0.  https://acp.copernicus.org/articles/3/1285/2003/acp-3-1285-2003.pdf
f.thorpe
CC BY-SA 4.0
2022-02-15T03:32:18.083Z
@f.thorpe So that means I can use the values of AK without converting? I am just confused, as they said in the manual that the  AKs for different units (e.g., DU or ppbv) are different.
Mala Pokhrel
CC BY-SA 4.0
2022-02-15T04:28:53.873Z
The AK would be different for DU vs ppbv since those units are not linearly proportional with altitude.  Before you use an AK, you have to convert your model data to the same layers as specified in the AK (discussed in the next page in that README).  To properly interpolate your vertical resolution to the satellite retrieval layers, you have to do a thickness-weighted averaging of model layer concentrations.  You can't just average the model layers that span the retrieval layers, since they likely have varying thicknesses.  Then you can compare model/sat w/ or w/o the AK... your choice.
f.thorpe
CC BY-SA 4.0
2022-02-15T04:29:50.983Z
If they provide AKs in ppbV, then no, you wouldn't have to convert to DU.
f.thorpe
CC BY-SA 4.0
2022-02-15T07:21:30.753Z
@f.thorpe Could you please elaborate  more on  thickness-weighted averaging of model layer? The AK values are in DU/DU so could give  coud you give me advice on how to convert as the value in ppbV ?
Mala Pokhrel
CC BY-SA 4.0
2022-02-15T15:42:09.710Z
Your model layers likely get thicker as you go up vertically...  so the upper model layers that are within the retrieval layer would have a larger contribution to the average.  For instance if model layer 5 is 1000m thick with 100 ppbV and layer 6 is 1500m with 200 ppbV, then a simple average would be 1000/2500 * 100 + 1500/2500 * 200 = 160 ppbV.  There's probably a more advanced way to do it, but at least this way you are weighting each layer by it's thickness when you average multiple model layers together to match the AK layers.
f.thorpe
CC BY-SA 4.0
2022-02-15T15:44:44.553Z
If the AKs are only in DU then you could convert the model data to DU and apply the AK.  After that you can convert back to ppbV if you want.  FYI I have not used the specific AKs  you are using so you may want to reach out to someone who works on the ozone retrievals or has direct experience with that product.
f.thorpe
CC BY-SA 4.0
2022-02-16T02:37:12.127Z
@f.thorpe Ok. Thank you for your help.
Mala Pokhrel
<atmosphere-modelling><satellites><validation>
How to convert units of averaging kernel from DU/DU to ppbv/ppbv
Mala Pokhrel
# How to convert units of averaging kernel from DU/DU to ppbv/ppbv

(Asked by: username_0 on 2022-02-04)

For validation of model data, I want to compare the ozone data from model to the satellite results downloaded from the [following link](https://avdc.gsfc.nasa.gov/pub/data/satellite/Aura/OMI/V03/L2/OMPROFOZ):

The satellite data are in DU(Dobson Unit) while the model data are in ppbv. To make them comparable, I converted the units of satellite data from DU to ppbv from the formula specified in the README file.

[![formula for conversion](https://i.sstatic.net/Pxkak.png)](https://i.sstatic.net/Pxkak.png)

But I have problem converting values of average kernel(AKs). The readme file specifies that

> Note the AKs for different units (e.g., DU or ppbv) are different, the DU/DU does not cancel out because the conversion from DU to ppbv varies with altitude (e.g. resulting from different T, P).

But, I am not sure what is the right way convert the values of Average Kernel from DU/DU to ppbv/ppbv so that I can use its values.

**Tags:** atmosphere-modelling, satellites, validation

> **Comments:**
> **username_1**: potentially related [Dobson unit](https://en.wikipedia.org/wiki/Dobson_unit)  
> **username_2**: If I understand your question, the averaging kernels aren't part of the conversion which is correct.  Instead, the averaging kernel is a unitless multiplier (should be near 1.0) that is applied at every layer.  You don't convert units of the AK because by definition it is unitless.  You can do the conversion without the AKs, and compare the biases with/without (as discussed in the link you provided).  
> **username_2**: Also see Figure 1 for an example of averaging kernels and how they are centered on 1.0.  https://acp.copernicus.org/articles/3/1285/2003/acp-3-1285-2003.pdf  
> **username_0**: @username_2 So that means I can use the values of AK without converting? I am just confused, as they said in the manual that the  AKs for different units (e.g., DU or ppbv) are different.  
> **username_2**: The AK would be different for DU vs ppbv since those units are not linearly proportional with altitude.  Before you use an AK, you have to convert your model data to the same layers as specified in the AK (discussed in the next page in that README).  To properly interpolate your vertical resolution to the satellite retrieval layers, you have to do a thickness-weighted averaging of model layer concentrations.  You can't just average the model layers that span the retrieval layers, since they likely have varying thicknesses.  Then you can compare model/sat w/ or w/o the AK... your choice.  
> **username_2**: If they provide AKs in ppbV, then no, you wouldn't have to convert to DU.  
> **username_0**: @username_2 Could you please elaborate  more on  thickness-weighted averaging of model layer? The AK values are in DU/DU so could give  coud you give me advice on how to convert as the value in ppbV ?  
> **username_2**: Your model layers likely get thicker as you go up vertically...  so the upper model layers that are within the retrieval layer would have a larger contribution to the average.  For instance if model layer 5 is 1000m thick with 100 ppbV and layer 6 is 1500m with 200 ppbV, then a simple average would be 1000/2500 * 100 + 1500/2500 * 200 = 160 ppbV.  There's probably a more advanced way to do it, but at least this way you are weighting each layer by it's thickness when you average multiple model layers together to match the AK layers.  
> **username_2**: If the AKs are only in DU then you could convert the model data to DU and apply the AK.  After that you can convert back to ppbV if you want.  FYI I have not used the specific AKs  you are using so you may want to reach out to someone who works on the ozone retrievals or has direct experience with that product.  
> **username_0**: @username_2 Ok. Thank you for your help.  

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## 0 answers

