Posted on January 5th, 2021

Clarification on Units for Maxar’s ACOMP Product

When ordering satellite imagery, there are a myriad of parameters that clients need to decide on with the assistance of Apollo Mapping. For several satellite imagery providers, one of those decisions is raw pixels values in Digital Numbers (DNs) or pixel values with an atmospheric correction.

Maxar, who operates the WorldView-1/2/3 and GeoEye-1 constellation, offers a proprietary atmospheric correction referred to as ACOMP. When ACOMP is applied to their satellite imagery, data is delivered in surface reflectance which is typically thought of as a percentage. As it is not possible to deliver a TIFF file with pixel values in percentage, Maxar has to transform the values to a scale that computers can handle. So we thought it would be useful to our readers to offer some advice on how to transform ACOMP pixel values into a percentage if required!

For most orders, your Maxar satellite imagery will be delivered with 16-bit depth meaning a possible range of pixel values from 0 to 2,047. And so accordingly, a pixel value of 0 represents 0% surface reflectance and 2,047 represents 100% surface reflectance. Going one step further, if your pixel value is 125 then the corresponding surface reflectance percentage is ~6.11% (or 125/2,048).

However, if you ordered four or eight-band multispectral WorldView-3 imagery along with eight-band short-wave infrared (SWIR), then your data will be scaled from 0 to 10,000 for the pixel values; and accordingly, 0% surface reflectance corresponds to a pixel value of 0, while 100% surface reflectance corresponds to a pixel value of 10,000.

We hope this helps our readers a bit and if you have any additional questions about transforming ACOMP values to surface reflectance percentage, feel free to drop us a line at any time to [email protected].

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