MAPPING THE SPATIAL DISTRIBUTION OF COLOMBIA’S FOREST ABOVEGROUND BIOMASS USING SAR AND OPTICAL DATA
<p><strong>Abstract.</strong> An assessment on the amount and spatial distribution of forest aboveground biomass (AGB) for the forests in Colombia was generated using in-situ national forest inventory data (IDEAM, 2018), in combination with multispectral optical data and synthetic aperture radar (SAR) satellite imagery. ALOS-2 PALSAR-2 gamma-0 backscatter annual mosaics (2015&ndash;2017) provided by JAXA were normalised and corrected using previous ALOS PALSAR annual mosaics (2007&ndash;2010) as reference. A multi-temporal Landsat 7 &amp; 8 composite over the whole of Colombia was used for the year 2016&thinsp;&plusmn;&thinsp;1. The national forest inventory in-situ plots used to train our model consisted of 5-subplots each and were collected during the period 2015&ndash;2017 in the main biomes of the country. A sample of permanent 1ha plots (PPMs) were also measured. Nationally developed allometries (Alvarez et al., 2012) were used to estimate AGB. A non-parametric random forests (RF) algorithm was used within a k-fold framework to retrieve AGB at 30&thinsp;m spatial resolution for the whole of Colombia. The algorithm was trained using forest inventory plots and validated at plot (0.35&thinsp;ha) and PPM level (1&thinsp;ha). The accuracy assessment found coefficients of determination (R<sup>2</sup>) of 0.68 and 0.61, and relative root mean square errors (Rel. RMSE) of 49% and 34% at plot and at PPM level, respectively. The results showed that the average AGB for the country was 118.1&thinsp;t&thinsp;ha<sup>&minus;1</sup> (45.6&thinsp;t&thinsp;ha<sup>&minus;1</sup> for Caribe, 75.4&thinsp;t&thinsp;ha<sup>&minus;1</sup> Andes, 122.5&thinsp;t&thinsp;ha<sup>&minus;1</sup> Pacifico, 32.7&thinsp;t&thinsp;ha<sup>&minus;1</sup> Orinoquia, and 200.5&thinsp;t&thinsp;ha<sup>&minus;1</sup> for the Amazonia, regionally), and that the total carbon stocks for the country were 6.7&thinsp;Pg C for the period 2015&ndash;2017.</p>