Spot 6 - Reflectance calibration

Question

I have a Spot-6 image and the metadata contain 9 values of SUN_ELEVATION (BottomRight BottomCenter BottomLeft CenterRight Center CenterLeft TopRight TopCenter TopLeft). I've used before Landsat and this contained 1 value of SUN_ELEVATION for use in the flectance equation. Now I don't know how will use these values in the equation to calculate sin(SUN_ELEVATION). How I should combine these values?

ANOTHER QUESTION IS ABOUT THE ESUN VALUES TO SPOT-6.. WHAT ARE THESE VALUES??.. WHERE ARE THERE??

The header for the first question is:

        <Located_Geometric_Values>
        <LOCATION_TYPE>TopRight</LOCATION_TYPE>
        <COL>23169</COL>
        <ROW>1</ROW>
        <TIME>2014-04-17T15:13:27.828000Z</TIME>
        <SATELLITE_ALTITUDE>701584.630405</SATELLITE_ALTITUDE>
        <Acquisition_Angles>
          <AZIMUTH_ANGLE>20.5991408203</AZIMUTH_ANGLE>
          <VIEWING_ANGLE_ACROSS_TRACK>-1.90302747221</VIEWING_ANGLE_ACROSS_TRACK>
          <VIEWING_ANGLE_ALONG_TRACK>12.12965768</VIEWING_ANGLE_ALONG_TRACK>
          <VIEWING_ANGLE>12.3394936579</VIEWING_ANGLE>
          <INCIDENCE_ANGLE_ALONG_TRACK>-12.8322522348</INCIDENCE_ANGLE_ALONG_TRACK>
          <INCIDENCE_ANGLE_ACROSS_TRACK>5.13233998335</INCIDENCE_ANGLE_ACROSS_TRACK>
          <INCIDENCE_ANGLE>13.7633382493</INCIDENCE_ANGLE>
        </Acquisition_Angles>
        <Solar_Incidences>
          <SUN_AZIMUTH>62.3148341003</SUN_AZIMUTH>
          <SUN_ELEVATION>54.9137375042</SUN_ELEVATION>
        </Solar_Incidences>
        <Ground_Sample_Distance>
          <GSD_ACROSS_TRACK>2.14080821911</GSD_ACROSS_TRACK>
          <GSD_ALONG_TRACK>2.3337350258</GSD_ALONG_TRACK>
        </Ground_Sample_Distance>
      </Located_Geometric_Values>
      <Located_Geometric_Values>
        <LOCATION_TYPE>CenterLeft</LOCATION_TYPE>
        <COL>1</COL>
        <ROW>5418</ROW>
        <TIME>2014-04-17T15:13:28.832000Z</TIME>
        <SATELLITE_ALTITUDE>701597.12665</SATELLITE_ALTITUDE>
        <Acquisition_Angles>
          <AZIMUTH_ANGLE>30.6025825529</AZIMUTH_ANGLE>
          <VIEWING_ANGLE_ACROSS_TRACK>-4.51029940362</VIEWING_ANGLE_ACROSS_TRACK>
          <VIEWING_ANGLE_ALONG_TRACK>12.7678042112</VIEWING_ANGLE_ALONG_TRACK>
          <VIEWING_ANGLE>13.6401205795</VIEWING_ANGLE>
          <INCIDENCE_ANGLE_ALONG_TRACK>-12.9524184599</INCIDENCE_ANGLE_ALONG_TRACK>
          <INCIDENCE_ANGLE_ACROSS_TRACK>8.10746086821</INCIDENCE_ANGLE_ACROSS_TRACK>
          <INCIDENCE_ANGLE>15.2135360829</INCIDENCE_ANGLE>
        </Acquisition_Angles>
        <Solar_Incidences>
          <SUN_AZIMUTH>62.4597352167</SUN_AZIMUTH>
          <SUN_ELEVATION>54.6058551573</SUN_ELEVATION>
        </Solar_Incidences>
        <Ground_Sample_Distance>
          <GSD_ACROSS_TRACK>2.16790984064</GSD_ACROSS_TRACK>
          <GSD_ALONG_TRACK>2.33122811517</GSD_ALONG_TRACK>
        </Ground_Sample_Distance>
      </Located_Geometric_Values>
      <Located_Geometric_Values>
        <LOCATION_TYPE>Center</LOCATION_TYPE>
        <COL>11586</COL>
        <ROW>5418</ROW>
        <TIME>2014-04-17T15:13:28.889000Z</TIME>
        <SATELLITE_ALTITUDE>701597.834082</SATELLITE_ALTITUDE>
        <Acquisition_Angles>
          <AZIMUTH_ANGLE>25.2806645718</AZIMUTH_ANGLE>
          <VIEWING_ANGLE_ACROSS_TRACK>-3.13630286198</VIEWING_ANGLE_ACROSS_TRACK>
          <VIEWING_ANGLE_ALONG_TRACK>12.4550951922</VIEWING_ANGLE_ALONG_TRACK>
          <VIEWING_ANGLE>12.9859855447</VIEWING_ANGLE>
          <INCIDENCE_ANGLE_ALONG_TRACK>-12.9212204779</INCIDENCE_ANGLE_ALONG_TRACK>
          <INCIDENCE_ANGLE_ACROSS_TRACK>6.38122383831</INCIDENCE_ANGLE_ACROSS_TRACK>
          <INCIDENCE_ANGLE>14.4843704031</INCIDENCE_ANGLE>
        </Acquisition_Angles>
        <Solar_Incidences>
          <SUN_AZIMUTH>62.3396191484</SUN_AZIMUTH>
          <SUN_ELEVATION>54.7446239807</SUN_ELEVATION>
        </Solar_Incidences>
        <Ground_Sample_Distance>
          <GSD_ACROSS_TRACK>2.14574425486</GSD_ACROSS_TRACK>
          <GSD_ALONG_TRACK>2.34669128077</GSD_ALONG_TRACK>
        </Ground_Sample_Distance>
      </Located_Geometric_Values>
      <Located_Geometric_Values>
        <LOCATION_TYPE>CenterRight</LOCATION_TYPE>
        <COL>23169</COL>
        <ROW>5418</ROW>
        <TIME>2014-04-17T15:13:28.945000Z</TIME>
        <SATELLITE_ALTITUDE>701598.530095</SATELLITE_ALTITUDE>
        <Acquisition_Angles>
          <AZIMUTH_ANGLE>19.9565074408</AZIMUTH_ANGLE>
          <VIEWING_ANGLE_ACROSS_TRACK>-1.76271955049</VIEWING_ANGLE_ACROSS_TRACK>
          <VIEWING_ANGLE_ALONG_TRACK>12.1425169852</VIEWING_ANGLE_ALONG_TRACK>
          <VIEWING_ANGLE>12.3332746441</VIEWING_ANGLE>
          <INCIDENCE_ANGLE_ALONG_TRACK>-12.8909872182</INCIDENCE_ANGLE_ALONG_TRACK>
          <INCIDENCE_ANGLE_ACROSS_TRACK>4.6455241327</INCIDENCE_ANGLE_ACROSS_TRACK>
          <INCIDENCE_ANGLE>13.7567884142</INCIDENCE_ANGLE>
        </Acquisition_Angles>
        <Solar_Incidences>
          <SUN_AZIMUTH>62.2195675283</SUN_AZIMUTH>
          <SUN_ELEVATION>54.8833713072</SUN_ELEVATION>
        </Solar_Incidences>
        <Ground_Sample_Distance>
          <GSD_ACROSS_TRACK>2.12313579954</GSD_ACROSS_TRACK>
          <GSD_ALONG_TRACK>2.36323624406</GSD_ALONG_TRACK>
        </Ground_Sample_Distance>
      </Located_Geometric_Values>
      <Located_Geometric_Values>
        <LOCATION_TYPE>BottomLeft</LOCATION_TYPE>
        <COL>1</COL>
        <ROW>10833</ROW>
        <TIME>2014-04-17T15:13:29.951000Z</TIME>
        <SATELLITE_ALTITUDE>701611.055334</SATELLITE_ALTITUDE>
        <Acquisition_Angles>
          <AZIMUTH_ANGLE>30.0393683451</AZIMUTH_ANGLE>
          <VIEWING_ANGLE_ACROSS_TRACK>-4.37063958883</VIEWING_ANGLE_ACROSS_TRACK>
          <VIEWING_ANGLE_ALONG_TRACK>12.7794685841</VIEWING_ANGLE_ALONG_TRACK>
          <VIEWING_ANGLE>13.609226307</VIEWING_ANGLE>
          <INCIDENCE_ANGLE_ALONG_TRACK>-12.9915180426</INCIDENCE_ANGLE_ALONG_TRACK>
          <INCIDENCE_ANGLE_ACROSS_TRACK>7.82212237621</INCIDENCE_ANGLE_ACROSS_TRACK>
          <INCIDENCE_ANGLE>15.1795500477</INCIDENCE_ANGLE>
        </Acquisition_Angles>
        <Solar_Incidences>
          <SUN_AZIMUTH>62.3651154507</SUN_AZIMUTH>
          <SUN_ELEVATION>54.5756410132</SUN_ELEVATION>
        </Solar_Incidences>
        <Ground_Sample_Distance>
          <GSD_ACROSS_TRACK>2.1593044921</GSD_ACROSS_TRACK>
          <GSD_ALONG_TRACK>2.33896262245</GSD_ALONG_TRACK>
        </Ground_Sample_Distance>
      </Located_Geometric_Values>
      <Located_Geometric_Values>
        <LOCATION_TYPE>BottomCenter</LOCATION_TYPE>
        <COL>11586</COL>
        <ROW>10833</ROW>
        <TIME>2014-04-17T15:13:30.006000Z</TIME>
        <SATELLITE_ALTITUDE>701611.745696</SATELLITE_ALTITUDE>
        <Acquisition_Angles>
          <AZIMUTH_ANGLE>24.6777067024</AZIMUTH_ANGLE>
          <VIEWING_ANGLE_ACROSS_TRACK>-2.99633305079</VIEWING_ANGLE_ACROSS_TRACK>
          <VIEWING_ANGLE_ALONG_TRACK>12.4673539097</VIEWING_ANGLE_ALONG_TRACK>
          <VIEWING_ANGLE>12.9674591697</VIEWING_ANGLE>
          <INCIDENCE_ANGLE_ALONG_TRACK>-12.9701540154</INCIDENCE_ANGLE_ALONG_TRACK>
          <INCIDENCE_ANGLE_ACROSS_TRACK>5.99494281947</INCIDENCE_ANGLE_ACROSS_TRACK>
          <INCIDENCE_ANGLE>14.4641360419</INCIDENCE_ANGLE>
        </Acquisition_Angles>
        <Solar_Incidences>
          <SUN_AZIMUTH>62.2446915519</SUN_AZIMUTH>
          <SUN_ELEVATION>54.7143402244</SUN_ELEVATION>
        </Solar_Incidences>
        <Ground_Sample_Distance>
          <GSD_ACROSS_TRACK>2.13259585466</GSD_ACROSS_TRACK>
          <GSD_ALONG_TRACK>2.36533405587</GSD_ALONG_TRACK>
        </Ground_Sample_Distance>
      </Located_Geometric_Values>
      <Located_Geometric_Values>
        <LOCATION_TYPE>BottomRight</LOCATION_TYPE>
        <COL>23169</COL>
        <ROW>10833</ROW>
        <TIME>2014-04-17T15:13:30.061000Z</TIME>
        <SATELLITE_ALTITUDE>701612.424576</SATELLITE_ALTITUDE>
        <Acquisition_Angles>
          <AZIMUTH_ANGLE>19.3139141146</AZIMUTH_ANGLE>
          <VIEWING_ANGLE_ACROSS_TRACK>-1.62244118348</VIEWING_ANGLE_ACROSS_TRACK>
          <VIEWING_ANGLE_ALONG_TRACK>12.1553682721</VIEWING_ANGLE_ALONG_TRACK>
          <VIEWING_ANGLE>12.3270833097</VIEWING_ANGLE>
          <INCIDENCE_ANGLE_ALONG_TRACK>-12.9497282578</INCIDENCE_ANGLE_ALONG_TRACK>
          <INCIDENCE_ANGLE_ACROSS_TRACK>4.15857053102</INCIDENCE_ANGLE_ACROSS_TRACK>
          <INCIDENCE_ANGLE>13.7502691903</INCIDENCE_ANGLE>
        </Acquisition_Angles>
        <Solar_Incidences>
          <SUN_AZIMUTH>62.1243336098</SUN_AZIMUTH>
          <SUN_ELEVATION>54.8530184038</SUN_ELEVATION>
        </Solar_Incidences>
        <Ground_Sample_Distance>
          <GSD_ACROSS_TRACK>2.10545648282</GSD_ACROSS_TRACK>
          <GSD_ALONG_TRACK>2.39275823656</GSD_ALONG_TRACK>
        </Ground_Sample_Distance>
      </Located_Geometric_Values>
    </Use_Area>   </Geometric_Data>

This sounds like an error in the header. Could you post the section in question? The sun elevation and sun angle should be scene center and associated with a single value. The swath size is not large enough to even require separate values for sun elevation as the would be quite uniform. I would imagine that if for some reason these values are valid your could just average them to acquire a single coefficient. — Jeffrey Evans, Sep 17, 2014 at 16:24
ok.. I've edited the question and added the piece of header of "DIM_SPOT6_xxxxxx.XML" — Pavel Angel Mendoza Villafane, Sep 17, 2014 at 20:05
Another question is about the ESUN values to SPOT-6.. what are these values?? where are there? — Pavel Angel Mendoza Villafane, Sep 17, 2014 at 20:37
ESUN is the earth/sun distance and it is not a coefficient in the header. It is a standard distance based on Julian date. Here is a spreadsheet that has the values. google.com/… — Jeffrey Evans, Sep 17, 2014 at 20:45
I referred to: solar exoatmospheric spectral irradiances of Spot 6. I seen that the reflectance equation is: rho=(PILdd)/(Eocos(SUN_ELEVATION)). Or maybe you know other equation for the SPOT-6?? — Pavel Angel Mendoza Villafane, Sep 17, 2014 at 20:48

Needs_Caffeine · Accepted Answer · 2022-09-21 11:43:48Z

1

It looks like you are trying to directly apply the radiometric calibration equations from the Landsat handbook to SPOT. The equations are slightly different because the DN calibration method is different. Take a look at the SPOT 5/6 handbook for the correct equations. You also want to use the solar zenith (not elevation) as the theta parameter.

Here is a paper that extends the reflectance radiometric calibration to include atmospheric correction.

edited Sep 21, 2022 at 11:43

Needs_Caffeine

697 bronze badges

answered Sep 18, 2014 at 14:17

Jeffrey Evans

30.2k2 gold badges46 silver badges93 bronze badges

Add a comment |

Stack Exchange Network

Spot 6 - Reflectance calibration

1 Answer 1

Your Answer

Not the answer you're looking for? Browse other questions tagged
remote-sensing
image
spot5
or ask your own question.

Hot Network Questions

Spot 6 - Reflectance calibration

1 Answer 1

Your Answer

Sign up or log in

Post as a guest

Not the answer you're looking for? Browse other questions tagged remote-sensingimagespot5 or ask your own question.

Related

Hot Network Questions

Not the answer you're looking for? Browse other questions tagged
remote-sensing
image
spot5
or ask your own question.