This MOD16 algorithm is developed for estimating the global evapotranspiration (ET) and is the core algorithm behind the MODIS ET product, which is original developed by NTSG.
Code Reference:
Mu, Q., Heinsch, F.A., Zhao, M., and Running, S.W. (2007). Development of a global evapotranspiration algorithm based on MODIS and global meteorology data. Remote Sensing of Environment 111, 519–536.
Mu, Q., Zhao, M., and Running, S.W. (2011). Improvements to a MODIS global terrestrial evapotranspiration algorithm. Remote Sensing of Environment 115, 1781–1800.
Zhang, K., Zhu, G., Ma, J., Yang, Y., Shang, S., and Gu, C. (2019). Parameter Analysis and Estimates for the MODIS Evapotranspiration Algorithm and Multiscale Verification. Water Resources Research 55, 2211–2231.