A computational framework to generate daily temperature maps using time-series of publicly available MODIS MOD11A2 product
Land Surface Temperature (LST) images (1 km resolution; 8-day composites) is illustrated using temperature measurements from
the national network of meteorological stations (159) in Croatia. The input data set contains 57,282 ground measurements of
daily temperature for the year 2008. Temperature was modeled as a function of latitude, longitude, distance from the sea,
elevation, time, insolation, and the MODIS LST images. The original rasters were first converted to principal components to
reduce noise and filter missing pixels in the LST images. The residual were next analyzed for spatio-temporal auto-correlation;
sum-metric separable variograms were fitted to account for zonal and geometric space-time anisotropy. The final predictions
were generated for time-slices of a 3D space-time cube, constructed in the R environment for statistical computing. The results show that the space-time regression model can explain a significant part
of the variation in station-data (84%). MODIS LST 8-day (cloud-free) images are unbiased estimator of the daily temperature,
but with relatively low precision (±4.1°C); however their added value is that they systematically improve detection of local
changes in land surface temperature due to local meteorological conditions and/or active heat sources (urban areas, land cover
classes). The results of 10–fold cross-validation show that use of spatio-temporal regression-kriging and incorporation of
time-series of remote sensing images leads to significantly more accurate maps of temperature than if plain spatial techniques
were used. The average (global) accuracy of mapping temperature was ±2.4°C. The regression-kriging explained 91% of variability
in daily temperatures, compared to 44% for ordinary kriging. Further software advancement—interactive space-time variogram
exploration and automated retrieval, resampling and filtering of MODIS images—are anticipated.
Keywords Land surface temperature – Regression-kriging – Space-time variogram – MODIS – Noise filtering – Principal component analysis