## 2 Materials and Methods  
### Study Area and Data Sources  
The study area is located in Yuxi City, Yunnan Province, China, between 23\({}^{\circ}\)19\({}^{\prime}\)-24\({}^{\circ}\)53\({}^{\prime}\) N and 101\({}^{\circ}\)16\({}^{\prime}\)-103\({}^{\circ}\)09\({}^{\prime}\) E. This area belongs tothe Southwest Forest Region, the second largest natural forest region in China. The terrain is mostly mountainous with steep slopes, complex topography, and limited accessibility. The region, with distinct dry and wet seasons and a predominantly dry climate, is also characterized by a variety of combustible materials and fire sources, making it a frequent and severely affected area for forest fires in China. The forest fire ignited at 15:27 on 11 April 2023, with the ignition point located in Hekou Village, Jiuxi Town, Jiangchuan District, Yuxi City. It was caused by the human practice of burning crop residues in the fields. The open flames were extinguished at 21:55 on 15 April, and the fire lasted for over four days. The burned area lies to the west of Yuxi City, bordered by Jiangchuan District to the southeast. The Dongbing River traverses through the entire region, with villages built along the mountainsides and scattered residential areas. The vegetation in the area consists primarily of a mixed forest of pine and broadleaf trees, dominated by Yunnan pine. This area is a typical wildland-urban interface, where fire prevention and control are both urgent and critical. The study of fire severity estimation holds significant practical implications for fire management in this region. The location of the study area is shown in Figure 1.  
The hyperspectral images were provided by the China Centre for Resources Satellite Data and Application ([[https://data.cresda.cn/](https://data.cresda.cn/)]([https://data.cresda.cn/](https://data.cresda.cn/)), accessed 20 December 2023). The ZY1-02D satellite was successfully launched on 12 September 2019 and carries visible-near-infrared and hyperspectral cameras that can effectively capture 9-band multispectral data with a 115 km swath width, as well as 166-band hyperspectral data with a 60 km swath width. The spatial resolution for the panchromatic band is up to 2.5 m, 10 m for multispectral, and 30 m for hyperspectral. The ZY1-02E satellite, launched on 26 December 2021, builds on the payloads of the ZY1-02D, adding a thermal infrared camera to capture 115 km wide, 16 m spatial resolution thermal infrared data. Both satellites operate in a sun-synchronous orbit in a coordinated phase arrangement, forming a dual-satellite network that significantly improves data acquisition efficiency and timeliness. The spectral range of the hyperspectral payloads on both the ZY1-02D and ZY1-02E satellites spans from 396 nm to 2485 nm, covering the visible (396 nm-700 nm), near-infrared (700 nm-1300 nm), and shortwave infrared (1300 nm-2485 nm) regions [42]. The hyperspectral data corresponding to the ZY1-02D satellite is designated as ZY1E, while the ZY1-02E satellite is designated as ZY1F. The pre- and post-fire image correspond to ZY1F and ZY1E, respectively. The spectral resolution in the visible-near-infrared range (396 nm-1032 nm) is 8 nm, and in the near-infrared to shortwave infrared range (1032 nm-2485 nm), is 16 nm. Sentinel-2 multispectral data (Sentinel-2 MSI L2A) with a 10 m spatial resolution was selected to estimate fire severity as verification data. The images were obtained from Google Earth Engine ([[https://code.eartheengine.google.com/](https://code.eartheengine.google.com/)]([https://code.eartheengine.google.com/](https://code.eartheengine.google.com/)), accessed 9 January 2024). Figure 2 shows the hyperspectral data cube image covering the burned area on 21 April 2023. The false-color image on the rectangular surface was synthesized using Band 33, Band 53, and Band 20 from the hyperspectral data, and the profile consists of 166 spectral bands.