New paper: Biases from incorrect reflectance convolution

01 May 2020

A recent paper from MONOCLE participant Olivier Burggraaff examines how to correctly apply the mathematical tool, spectral convolution, to reduce the overall error when comparing data sets from different sensors resulting in improved data products for earth observation.


Reflectance, a crucial earth observation variable, is converted from hyperspectral to multispectral through convolution. This is done to combine time series, validate instruments, and apply retrieval algorithms. However, convolution is often done incorrectly, with reflectance itself convolved rather than the underlying (ir)radiances. Here, the resulting error is quantified for simulated and real multispectral instruments, using 18 radiometric data sets (N = 1799 spectra). Biases up to 5% are found, the exact value depending on the spectrum and band response. This significantly affects extended time series and instrument validation, and is similar in magnitude to errors seen in previous validation studies. Post-hoc correction is impossible, but correctly convolving (ir)radiances prevents this error entirely. This requires publication of original data alongside reflectance.

Read the full paper in Optics Express