Monitoring crop and vegetation water demand
Agricultural land use planning and zoning benefits significantly from having information on irrigated versus non-irrigated areas available. In combination with information on crop evapotranspiration and crop water productivity, operational irrigation management guidance can be provided during project implementation and during project review.
The impact of water and irrigation management interventions can also be assessed with quantitative EO-based information. When crop type has been mapped, crop-specific water footprint accounting is possible, optimizing crop production over large areas at high detail. This also enables the identification of areas with water logging or faulty irrigation equipment, or prompt better field levelling.
This service will focus on mapping and monitoring of irrigated versus non-irrigated crop area, as well as what specific crop types grow where, and how crop stages develop over time. This can include field preparation such as ploughing and flooding, seeding/transplanting, vegetative and reproductive stages, and crop harvest timing.
Typical crop mapping and monitoring products are produced using optical and radar sensors with medium revisit rates (e.g. Sentinel-1, Sentinel-2, Landsat, SPOT). Estimates of crop evapotranspiration can be provided for all crops in general, without crop distinction, or for specific crops. In a similar way, biomass production and yield prognosis can be provided. Finally, crop water productivity provides. This type of information can be provided using Sentinel-2, Landsat at 10-30m and MODIS-type sensors at 250m.
Known Limitations
Radar imagery is well suited for frequent observations of dynamic processes such as irrigation and crop stage development. The geographic and temporal coverage, however, should be assessed per country. Historical radar image available is typically fragmented in time and space, while current radar observations still do not consistently cover all countries of interest. Moreover, the information content of the available imagery may vary per country, as the Sentinel-1 observation schedule has fixed observation modes and intervals over predefined areas.
Radar data cannot be used for monitoring of evapotranspiration. Optical imagery, when associated thermal information is available, is suitable for evapotranspiration monitoring, but it cannot deliver frequent observations in persistently cloudy areas. Finally, the mapping of smallholder crop type and performance is very challenging, accurate crop classification of small fields cannot always be guaranteed.
Future Enhancements
Denser time series stemming from Sentinel 1+2 will provide enhanced capacity for monitoring crop and vegetation developments at high spatial and temporal resolution needed to capture field patters and within season vegetation growth stages. In addition Sentinel-3 will acquire thermal imagery at 1 km resolution on near daily time steps. This resolution is similar to MODIS so the additional gains for temperature based applications (cf. ET mapping) may come in further developments for downscaling the 1 km data to the Sentinel 1/2 resolution using e.g. the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM). Finally, specification are currently being discussed regarding the design of new high resolution thermal sensors but this to be regarded as a longer term development perspective (+10 years).
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