Normalized Difference Latent Heat Index for Remote Sensing of Land Surface Energy Fluxes

Latent heat is the energy released or absorbed by a substance through phase change without changing its temperature. Its flux is a crucial element of the hydrological cycle at the land-air interface. Many water-related indexes have been proposed as indicators for latent heat flux extraction from satellite imagery, while the extraction accuracy still remains a space to improve nowadays. In this paper, a new multiband index, called normalized difference latent heat index (NDLI), is proposed for remote sensing of land surface heat flux. It utilizes the reflectance observations of three bands from Landsat 8 operational land imager, including red, green, and shortwave infrared channels. Its performance in terms of deriving latent heat flux through their incorporation into the commonly used surface energy balance algorithm for land (SEBAL) is then compared with the other three existing water-related indexes with two of them using normalized difference water index and normalized difference vegetation index. Results show that NDLI exhibits the strongest correlation with the SEBAL-derived latent heat flux among the used water-related indexes with correlation coefficient $r = 0.75$. They also indicate that the NDLI is the most sensitive and reliable index outperforming the previously developed indexes to determine the characteristics of water content in different land cover types. It is concluded that NDLI can be used as a good indicator to represent the potential latent heat flux at the earth's surface.