TOA and SREF value range

[Roberta Fagandini]

Hi all,

I processed this Sentinel 2 image (S2A_MSIL1C_20170703T101021_N0205_R022_T32TQR_20170703T101041) using arcsi and I'm not sure about the meaning of surface reflectance values resulting from the SREF computation. The minimum value is 1 while the maximum is 1910 (3rd quartile: 72). We processed the same image using sen2cor 2.3.1 and the range value is completely different (min=1 and max=21864, 3rd quartile: 705).

I have already searched for an answer in previous posts but I'm still a bit confused. I read that reflectance is multiplied by 10000 while in another post the multiplier is 1000. Which multiplier is actually used by arcsi?

And what about the TOA values computed by arcsi? They seem to be divided by 10 compared to the values of the original bands.

Can someone provide further information about TOA and SREF value range?

Thanks,

Roberta  

[Pete Bunting [pfb]]

Hi Roberta,

The default scale factor used within ARCSI is 1000 and controlled by the —scalefac switch. The TOA product from sentinel-2 is rescaled to the arcsi scale factor.

Zero is used as the no data value for images outputted from ARCSI so 1 is therefore the minimum valid pixel value.

Best wishes,

Pete

****************************************************
* Dr Pete Bunting
* Reader in Remote Sensing
* Earth Observation and Ecosystem Dynamics Group
* Department of Geography and Earth Sciences
* Aberystwyth University
* Aberystwyth
* Ceredigion
* SY23 3DB
* UK
*
* Ph: +44 (0) 1970 622615
* Mob: +44 (0) 7917 842743
* Email: p...@aber.ac.uk
* ORCID: http://orcid.org/0000-0002-7435-0148
****************************************************
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> On 25 Aug 2017, at 11:15, Roberta Fagandini <robifa...@gmail.com> wrote:
>
> Hi all,

> I processed this Sentinel 2 image (S2A_MSIL1C_20170703T101021_N0205_R022_T32TQR_20170703T101041) using arcsi and I'm not sure about the meaning of surface reflectance values from the SREF computation. The minimum value is 1 while the maxiumum is 1910.
> I have already searched the answer in previous posts but I'm still a bit confused. I read that reflectance is multiplied by 10000 while in another post the multiplier is 1000. What's the correct one?

>
> And what about the TOA values computed by arcsi? They seem to be divided by 10 compared to the values of the original bands.
>
> Can someone provide further information about TOA and SREF value range?
>
> Thanks,
>
> Roberta
>

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[Markus Neteler]

Hi Pete,

thanks for the clarification.
Would you mind to add the "Default 1000) hint to the help text?

# old
--scalefac SCALEFAC Specifies the scale factor for the reflectance
products.

# new
--scalefac SCALEFAC Specifies the scale factor for the reflectance
products. (Default 1000)

as it already is given for --cs_initdist and a few other switches?

thanks
Markus

[Pete Bunting [pfb]]

Thanks Markus, 

I’ve added so it’ll be in the next release. 

Best wishes, 

Pete

****************************************************
* Dr Pete Bunting
* Reader in Remote Sensing
* Earth Observation and Ecosystem Dynamics Group
* Department of Geography and Earth Sciences
* Aberystwyth University
* Aberystwyth
* Ceredigion
* SY23 3DB
* UK
* 
* Ph: +44 (0) 1970 622615
* Mob: +44 (0) 7917 842743
* Email: p...@aber.ac.uk
* ORCID: http://orcid.org/0000-0002-7435-0148
****************************************************

"Please consider the environment before printing this email or any documents attached”