*2.3. Airborne Hyperspectral HySpex Data*

Aerial hyperspectral data were obtained by MGGP Aero Sp. z o.o. on 29 August 2017 using sensors located on a Cessna 402B aircraft. A hyperspectral image with a 16-bit radiometric resolution was recorded with two HySpex Visible and Near Infrared (VNIR-1800) scanners and a Shortwave Infrared (SWIR-384) scanner. The specification of both sensors is provided in the table below (Table 1).


**Table 1.** Main technical characteristics of HySpex scanners used in this work.

<sup>1</sup> A number of spectral bands were deleted due to overlapping spectral ranges between VNIR-1800 and SWIR-384 sensors. <sup>2</sup> a number of pixels per scan line.

The aerial hyperspectral images were prepared for further processing in accordance with the diagram presented in the schema (Figure 3). The data obtained by hyperspectral sensors were converted to radiance units with HySpex RAD software. Then, the hyperspectral image was subjected to geometric correction, which employed the digital surface model in PARGE (PARametric GEocoding) software (ReSe Applications LLC, Wil, Switzerland), and atmospheric correction was performed with the MODTRAN5 model in ATCOR4 (ATmospheric CORrection) software (ReSe Applications LLC, Wil, Switzerland). Nine flight lines were mosaicked and re-sampled to achieve a uniform spatial resolution of 1 m. Next, the last 21 bands in the SWIR range were removed because of the high level of noise caused by the sensor's lower SNR (Signal to Noise Ratio) at the extreme ranges of the imaged spectrum, which ultimately resulted in a 430-band image in the spectral range of 416.18–2396.44 nm.

**Figure 3.** Research algorithm.

In order to reduce HySpex data dimensionality, Minimum Noise Fraction (MNF) transformation was applied. Based on MNF bands, eigenvalues, and visual assessment of transformed bands, the first 30 MNF bands were selected for further processing. Finally, two data sets were prepared for species classification: the first one contained 430 HySpex bands while the second one contained 30 MNF bands.
