Graphic method for retrieval of quantitative data from computer-mapped qualitative information, with a NASA video as an example

In Earth science, original data elaboration is often very complex and the results are generally provided in the form of (computer-made) maps, a qualitative representation. The aim of this paper is to illustrate a graphic method of analysis that allows the reverse: tracing back, on scientific bases, quantitative data from computer-mapped information, by using widely-available graphic tools, including an estimate of the precision of the numerical outcomes. That may be needed, e.g., for independent evaluation of published data or, for comparison with new elaborations. A NASA video was used as an example, reconstructing the maps of the Earth surface yearly from 1998 to 2017. Static frames were extracted from it and used to obtain numerical data on the evolution of the min/max snow/ice-covered land/sea surfaces, separately for the two hemispheres. The use of the proposed method allows concerned scientists to obtain the quantitative values of the relevant data, including an uncertainty estimate, e.g., in order to compare them with those found in the literature and on websites. The paper focuses on the map-analysis method, and on the metrological evaluation of the uncertainty of the retrieved data. Finally, some quantitative results are commented and found consistent with literature data on the same subject matter.