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Extracting Inputs to the Atmospheric Correction in a Planetscope or Skysat Surface Reflectance Image

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Rafael Ricardo Bastidas Mendez

Associated metadata describing inputs to the correction is included in a GeoTIFF ImageDescription metadata header as a JSON encoded string. With Python, you have the capability to extract these inputs from PlanetScope or SkySat image products, specifically the atmospherically corrected surface reflectance products:

import rasterio
import json

filename = rasterio.open('20210913_211131_ssc15_u0001_analytic_SR.tif') #item ID: PlanetScope or SkySat

tags = filename.tags()['TIFFTAG_IMAGEDESCRIPTION']
jtags = json.loads(tags)
atm_inputs = jtags['atmospheric_correction']
print ("atmospheric correction", json.dumps(atm_inputs, indent=4))

Output:

Screen_Shot_2021-10-14_at_9.46.32_AM.png

Read more about Planet's Surface Reflectance product.

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4 comments
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  • Avatar
    Braun Rémi
    (Edited )

    Hello,

    I have some SkySat Collect product pansharpened without any reflectance coefficients.

    I don't see any documentation about this, so I don't even know what is the units of these products.

    Here is the content of the product:

    And the tags:

    TIFFTAG_IMAGEDESCRIPTION={"properties": {"satellite_azimuth": 91.31511529166666, "satellite_elevation": 82.70983409111109, "sun_azimuth": 108.02678554722222, "sun_elevation": 61.958094182222226}

    Do you know something about this ?

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  • Avatar
    Rafael Ricardo Bastidas Mendez

    Hello Braun,

    Thank you for your comment. The reflectance coefficients for SkySat are available for products that have been transformed to Top of Atmosphere radiance. (ortho_analytic, ortho_panchromatic). For 20201223_220311_ssc13_u0002, the reflectance coefficients are:

    Panchromatic: "reflectance_coefficients": [2.1774764118470272e-05]

    Analytic radiance (TOAR): "reflectance_coefficients": [1.7138619391877836e-05, 1.8910223621257227e-05, 2.17299756251008e-05, 3.105477468010073e-05]

    The pansharpened data does not have meaningful radiometric units (They are uncalibrated). You can find more info about SkySat products at https://developers.planet.com/docs/data/skysat/

    I hope you find this helpful. If we can be of any further assistance, please let us know.

    Thank you!

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  • Avatar
    Braun Rémi

    Ok, thanks for for quick response :)

    So, if I understand correctly, it makes no sense to try to get pansharpen data in reflectance, I should leave them in DN ?

     

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  • Avatar
    Rafael Ricardo Bastidas Mendez

    Hi Braun,

    Thank you for reaching out. For Planet images that's correct. Pansharpened products are designed for multispectral applications which require highest available resolution and accurate geolocation and cartographic projection. If you need reflectance pixel values in a SkySat collect, I would recommend to download the surface reflectance product.  

    If you have any more questions, please let us know. :) 

    Thank you! 

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