Possibilities of the Application of the Medium-Resolution Landsat 8 and the High-Resolution RapidEye Optical Imagery in Visualization and Detection of Changes in the Forest Cover by Windthrows

U radu su dani prikaz i usporedba satelitskih informacija srednje (Landsat 8, 30 m) i visoke (RapidEye, 5 m) rezolucije radi ispitivanja mogućnosti vizualne i kvantitativne procjene šteta od vjetroizvala na Medvednici, nakon oluje Teodor u studenome 2013. godine, te obnove šumskog pokrova u 2018., odnosno nakon pet godina. Za vizualnu detekciju šteta na čitavom području korišten je 3D prikaz, u 15 m prostornoj rezoluciji, izveden iz RGB kanala vidljivog dijela spektra, izoštren pomoću pankromatskoga kanala. Prostorna razlučivost različitih satelitskih indeksa (NDVI, SAVI, MSAVI, NDMI, NBR, NBR2), kao kvantitativne mjere stanja vegetacijskog pokrova, ispitivana je na temelju snimaka Landsat 8 na čitavom području Medvednice. Od ispitivanih indeksa najbolja razlučivost vegetacijskog pokrova postignuta je na korigiranim SAVI i MSAVI indeksima u odnosu na NDVI, dok su indeksi temeljeni na infracrvenom dijelu spektra (NDMI, NBR, NBR2) pokazali dosta dobru osjetljivost pri detekciji narušenosti šumskog pokrova nakon vjetroizvala. Na ispitivanom dijelu površine s vjetroizvalom, neposredno uz potok Bliznec, utvrđena je znatna komparativna prednost snimaka visoke rezolucije (RapidEye) pri razlučivanju šteta na pokrovu odnosno pri praćenju stanja obnove šumske vegetacije. Na osnovi dobivenih prethodnih rezultata utvrđene su znatne mogućnosti satelitskih snimaka srednje i visoke rezolucije, kako u svrhu detekcije šteta nakon prirodne nepogode, tako i pri praćenju obnove šuma na tim površinama, što će potvrditi daljnji tijek ovog istraživanja.This paper presents a comparison of the satellite information of medium (Landsat 8, 30 m) and high (RapidEye, 5 m) resolutions for the purpose of examining the visual and quantitative estimates of wind damages and the renovation of the forest cover following the Theodor storm in November 2013 in Medvednica mountain, North-western Croatia. 3D visualization of the whole Medvednica area was derived from the Landsat 8 RGB channels of the visible part of the spectrum, pan-sharpened with the panchromatic channel on 15 m spatial resolution for visual forest damages detection. The spatial sensitivity of different satellite indices (NDVI, SAVI, MSAVI, NDMI, NBR, NBR2), based on Landsat 8 imagery, as a quantitative measure of the state of the vegetation cover, was investigated throughout the whole Medvednica area. From the investigated indices, the best detection of the changes in the forest cover was achieved by soil corrected indices such as SAVI and MSAVI in relation to the standard NDVI index. Indices based on the infra-red part of the spectra (NDMI, NBR, NBR2) showed quite good performance in detection of the damages of the forest cover. By the comparative assessment on the chosen pilot area with severe windthrows near Bliznec, a significant advantage of the high-resolution RapidEye imagery in comparison with Landsat 8, was confirmed for the potential purpose of the more precise silvicultural subgroups delineation and monitoring of the success of the restoration of the young forest cover. Based on the obtained results, substantial possibilities of medium and high-resolution satellite imagery have been identified, both for the purpose of damages assessment after natural disasters and for the monitoring of the reforestation on these surfaces, which will be confirmed in the further course of this research