Dark Object Subtraction using Top of Atmosphere Reflectance?

Question

I'm working on a WorldView 3 image in QGIS and have been told to use Dark Object Subtraction (DOS) to atmospherically correct it to surface reflectance using the raster calculator. I have the Top of Atmosphere (TOA) reflectance and the original Digital Number (DN) image.

I have only been able to find guides and papers (e.g. Song et al 2001 Classification and Change Detection Using Landsat TM Data: When and How to Correct Atmospheric Effects? and Chavez 1988 An improved dark-object subtraction technique for atmospheric scattering correction of multispectral data) using DN values to calculate path radiance. These don't use TOA reflectance.

As I have TOA reflectance if I identify dark objects and subtract the mean TOA reflectance value of these from the image would this be a valid DOS method?

Answer 1

Dark object subtraction is not atmospheric correction. It is image normalization. It is the simplest way of making two images acquired at different times, with different atmospheric conditions and view angles resemble eachother spectrally.

As such, what you get is not a 'correct surface reflectance value'. What you get is something that may, or may not, help you compare images from different times.

With the above in mind, yes, you would get 'DOS-corrected surface reflectance values' from that approach, but they should not be used for physical modelling or comparison with reflective spectra from the literature, as these things require actual atmospherically corrected data.

With your edits in mind - yes, DOS correction can be done on TOA reflectance data, and you simply do it by finding one or more dark objects and subtracting their value (or average value) from the original TOA reflectance. You should also consider what impact negative values will have on your further use of the data, and if they should be set to 0 instead.

Answer 2

DOS (dark object subtraction) method is the simplest atmospheric correction method. It can be applied TOA reflectance band by band. Dark object can be defined as the darkest pixel and pixels. But it should be noted that the validity of dark objects because sometimes they are not so dark, for example the turbid water body. you can also check the developer reply to DOS method.