The above information can be collected with remote sensing. Collection of spectral data can allow the calculation of indices that give an estimate of the plant condition, or can distinguish the crops plants from weeds. Vegetation and soil moisture or temperature can also be measured by remote sensors that are mounted on a combine. Crop yields can be estimated directly from a vegetation index, or with the use of additional data (moisture, temperature, historic data) can be estimated with the use of complex mathematical models.