# Remote Sensing for Irrigation of Horticultural Crops
## 3 Sensors and Platforms
### Remote Sensing Platforms
#### 3.2.1 Satellite
[PERSON] and [PERSON] [34] reported on new satellite technologies related to microsatellites and nanosatellites, which increment the number of observations by sharing the same orbit. One of the first examples comes from Planet Labs, which launched four prototype satellites in order to test the performance of the system [34]. Satellite constellations (Landsat, SPOT, Global Navigation Satellite System and GeoEye/WorldView families; Rapid Eye) have identical satellites positioned on the same orbit to diminish the revisit time [52; 53]. Satellite that operate in dual mode are defined as a constellation, such as GOCE and the dual GRACE satellites launched in 2009 to measure the gravitational field of the Earth [54]. In the recent past, satellites were characterized by a low spatial resolution and were used for several purposes over large geographic areas, but were unable to assess crop yield variability within a field [48]. Single satellite based systems continue to improve in imaging performance, including better spatial and spectral resolution as well as sensor agility, so in-track and cross-track stereo capture is available [55]. Currently, new opportunities for mapping and monitoring crop yield variability are provided by high-resolution satellite sensors (e.g., SPOT 6 and 7, Ikonos, Quick-Bird) that have narrowed the gap between image by satellite and by airborne vehicles [56; 57]. Landsat series from 1 to 7, for example, had a spatial resolution ranging from 30 to 79 m and a radiometric resolution of 6-8 bits, usable to some extent for mapping water quality parameters [58; 59; 60]. Landsat 8 (12-bit radiometric resolution) is suitable for remote sensing of water in lakes (even dark with CDOM-rich); although the revisit time of 16 days limits its use in routine monitoring of water body quality. Since satellite measurements are not satisfactory for monitoring diurnal variation, [PERSON] et al. [62] noted advantages from the use of electromagnetic waves constantly released by the Global Navigation Satellite System (GNSS) satellite constellations for retrieving different geophysical parameters of the Earth's surface. For irrigation purposes, GNSS reflectometry (GNSS-R) system is useful for soil moisture monitoring, because it is able to monitor diurnal variation [62]. Satellite missions, labelled Sentinel 1 up to 5, were set up for environmental monitoring [63]. The launch of Sentinel-2 in 2015 opened a new era in remote sensing. This system has a medium spatial resolution, super-spectral instrument with a field of view of 290 km, a revisit capability of 5 days (two satellites), a resolution of 10 m, 20 m and 60 m, and a moderately large band set (13 spectral bands) aiming to provide global land coverage. The mission ensures continuity of the previous missions (Landsat and SPOT) and provides geochemical and physical variables, land cover maps and land change detection maps. Its image spatial resolution (from 60 m to 10 m) allows the monitoring of several small water bodies as reported by [PERSON] et al. [64], who have shown that Sentinel-2 was able to map water quality. It may monitor Chlorophyll a (Chl a) as an indicator of phytoplankton, Chromophoric (or colored) Dissolved Organic Materials, and Dissolved Organic Material concentrations. [PERSON] et al. [65] have assessed the suitability of Sentinel 2 data in agriculture for land cover classifications. Results appeared encouraging, although the classification results for the pixel- and