Initially, estimates of senescence were via descriptions of flower growth stages. Later, colour photo guides were used. These techniques have variable accuracy as data providers often give car seat estimates and have very little training to ensure consistency. 2.6 Environmental models Rainfall amount is the key determinant of crop and pasture growth. Models to predict growth and yield are usually dependant on the relevant growing season rainfall and subsequent evaporation.
Several models exist which estimate grassland curing using rainfall and temperature data.
The models have had limited operational use to date but further investigation of crop and pasture production and maturity models may provide a vital link between visual estimates and satellites. The predictive capability of models is important due to the time delay in scanning with high resolution satellites. For over a decade remote sensing instruments have used the properties of active chlorophyll in growing plants to effectively assist in the estimation of fuel moisture and curing. Most pastures and crops respond to visible light by absorbing red and blue light from the sun for photosynthesis and reflect green light which is detected by the human eye as leaf colour. Visible light is just a small portion of the electromagnetic spectrum and right across the spectrum healthy vegetation absorbs and reflects light.