Table 1 Summary of environmental data considered when fitting binary logistic and negative binomial geostatistical models to tsetse catch data
Environmental variable | Trap data range | Source | Spatial resolution (m) | Time period | Derivation |
|---|---|---|---|---|---|
Enhanced vegetation index (EVI) | 0.07–0.19 | Landsat 5 | 30 | December 2009 | \( \left\{\frac{NIR- Red}{NIR+6\times RED-7.5\times BLUE+1}\right\} \) |
Soil Moisture Index (SMI) | 0.33–0.64 | Landsat 5 | 30 | December 2009 | \( \frac{Tsmax- Ts}{Tsmax- Ts min} \), where Tsmax and Tsmin are the maximum and minimum surface temperatures for a given Normalised Difference Vegetation Index (NDVI) value. See Wang et al. [38] |
At-satellite brightness temperature (°C) | 25.1–28.9 | Landsat 5 | 30 | December 2009 | Thermal Infrared Sensor (TIRS) band i.e. Band 6 |
Land surface temperature (LST) | 27.9–34.5 | Landsat 5 | 30 | December 2009 | At-satellite brightness temperature and NDVI were used to derive LST. Details on the algorithms used can be found in Ndossi et al. [39] |
Elevation (m) | 852–1210 | Shuttle Radar Topography Mission (SRTM) | 30 | 2000 | SRTM Void Filled data |
Slope (°) | 0–7.8 | Shuttle Radar Topography Mission (SRTM) | 30 | 2000 | Derived from SRTM elevation data using the hydrology tools within the Spatial Analyst Toolbox of ArcGIS (version 10.3.1) |
Flow accumulation | 0–1451 | Shuttle Radar Topography Mission (SRTM) | 30 | 2000 | Derived from SRTM elevation data using the hydrology tools within the Spatial Analyst Toolbox of ArcGIS (version 10.3.1) |
Fragmentation indices | Various | Advanced Spacebourne Thermal Emission and Reflection Radiometer (ASTER) | 15 | December 2010 | Calculate Normalised Difference Vegetation Index, i.e. \( NDVI=\frac{NIR- Red}{NIR+ Red} \) and using a threshold of 0, designate pixels as either vegetated or not vegetated. The R package SDMTools was then used to derive the following patch statistics within 350 m of the trap: • Average distance between patches • Maximum distance between patches • Number of patches • Area covered by patches • Size of largest patch |