Rapeseed crop damage by wildlife assessed from Landsat images

Absztrakt

Rapeseed is the fourth most important crop in Hungary regarding its cultivation area. Crop damage by deer and boar has been becoming strongly debated issue in the last few years. More exact clarification of damage was aimed at in this study with help of Landast images. Six rapeseed fields were investigated both in 2012 and 2013 in the administrative area of Várfölde, Bánokszentgyörgy, Bázakerettye and Borsfa (Zala County, Hungary). The total area in 2013 was 43 hectares. 100 % wildlife damage affected 3.9 hectares and 10 hectares were free from any damage. The total area in 2012 was 40 hectares in which 3.3 hectares were free from damage but neither fields suffered total damage. Yield map from 2017 of a 26 hectares field near to Gutorfölde and Szentkozmadombja was used to validate the space image based assessment method with real yield data. Landsat 7 images with acquisition dates of 2013.04.16., 2013.05.18. and 2013.06.03. were downloaded from the website of US Geological Service.  All bands and NDVI index were investigated for all dates to establish best estimator for differences between damaged and not damaged fields. Band 5 (SWIR: 1.55-1.75 μm) in 16^th of April proved to be the best.  It was concluded with help of the reflectance data (zero damage: 96.4, complete damage:164.5, partial damage:124.7 on the average) that yield reduction was 41.5 % on areas with partial damage. There was no complete damage in 2012. However, reflectance data of not damaged fields were very close to each other in the two years (96.4 in 2013 and 89.9 in 2012 on the average) thus, it could be assumed that the same is true for reflectance data of completely damaged fields, so data from 2013 can be used for the comparison. Based on the data (zero damage: 89.9/2012, complete damage:164.5/2013, partial damage:118.4/2012 on the average) it was calculated, that one field suffered 38 % yield reduction, one hectare portion of another field suffered 23 % yield reduction, and other fields were not damaged significantly. Yield map from 2017 and Landsat 8 SWIR reflectance (Band 6: 1.566 – 1.651 μm) in 3^rd of April have shown strong correlation (R²=0,634), which was a direct evidence that both yield and wildlife damage of rapeseed can be reliably assessed from Landsat SWIR reflectance data acquired in April.