Chapter 7

Satellite Remote Sensing in Precision Agriculture

Multispectral Satellites

Nearly all multispectral satellites collect imagery at blue, green, red, and near-infrared (NIR) wavelengths; the bandwidths are generally between 35 and 200 nm. Narrower bandwidths (higher spectral resolution), in general, provide a greater ability to discriminate between different types of factors that cause crop stress (e.g., crop deficiencies due to nitrogen or phosphorus). Multispectral satellites may also collect reflectance at the yellow and red edge (RE) and other NIR wavelengths. Red edge reflectance occurs from 680 to 750 nm between the R and near-infrared (NIR) wavelengths. It is the region where reflectance increases dramatically as chlorophyll absorption decreases. The short-wave infrared (SWIR) and thermal IR (ITR) capabilities also exist on some multispectral remote sensing satellites, and these bands are often useful for estimating crop residue cover or crop water stress, although the utility of TIR bands is diminished because of coarse spatial resolution (120 m for Landsat 8). 

Flock Dove

The PlanetScope Dove satellite constellation holds the world record of the most satellites launched at once from one rocket and will collect imagery up to 2 million km² per day. The satellite constellation is operated by Planet Labs PBC. 120+ nanosatellites called Doves, weighing only 5.8 kg each, provide 3-meter multispectral image resolution for a variety of mapping applications, including several humanitarian and environmental applications, from monitoring deforestation and urbanization to improving natural disaster relief, and agricultural yields around the world. The constellation revisits more frequently than any existing government or commercial satellites.

GeoEye-1

GeoEye-1 sensor has a panchromatic band and four multispectral bands (blue, green, red, and near-infrared, at 1.65 meters). The sensor has the ability to rotate in any direction and can acquire images up to 60 degrees off-nadir. GeoEye-1 data is very useful for studying surface conditions on a fine scale. Its short return interval (3 days) is also advantageous for observing changing conditions and increases the chance of getting cloud and smoke-free scenes. The panchromatic band has a spatial resolution of 0.41 meters at nadir.

KOMPSAT-3

KOMPSAT-3 is an optical high-resolution Korean observation mission of KARI (Korea Aerospace Research Institute). The objective is to provide high-resolution optical imagery required for GIS (geographical information systems), as well as other environmental, agricultural, and global climate change applications. KompSat 3 imagery has been used infrequently for agricultural applications. The high-resolution imaging satellite carries a camera that will resolve objects as small as 70 cm, or 2.3 feet, on Earth's surface.

lKONOS-2

IKONOS-2 was an Earth-imaging satellite of DigitalGlobe Inc., which launched in 1999 and ceased operations in 2015. With an altitude of 681 km and a revisit time of approximately 3 days, IKONOS produces one-meter panchromatic and four-meter multispectral imagery that can be combined to accommodate a wide range of high-resolution imagery applications.

Landsat 7 an 8

Landsat 7 satellite carries the Enhanced Thematic Mapper Plus (ETM+) sensor. This instrument was improved from previous instrumentation designs. The primary features on Landsat 7 include a panchromatic band with 15-meter spatial resolution, an onboard full aperture solar calibrator, five percent absolute radiometric calibration, and a thermal infrared channel with a four-fold improvement in spatial resolution over Thematic Mapper (TM).

Pleiades-A and B

The Pleiades-!A and 1B satellites can provide orthorectified color data at 0.5-meter resolution (roughly comparable to GeoEye-1) and revisit any point on Earth as it covers a total of 1 million square kilometers (approximately 386,102 square miles) daily. Perhaps most importantly, Pleiades-1 is capable of acquiring high-resolution stereo imagery in just one pass and can accommodate large areas (up to 1,000 km x 1,000 km). The Pleiades-1A satellite features four spectral bands (blue, green, red, and IR) and image location accuracy of 3 meters (CE90) without ground control points. Image location accuracy can be improved even further—up to an exceptional 1 meter—by the use of ground control points (GCPs).

QuickBird

QuickBird was a private satellite operated by DigitalGlobe providing data from 2001 to 2015. The satellite collected panchromatic (black and white) imagery at 61-centimeter resolution and multispectral imagery at 2.44- (at 450 km) to 1.63-meter (at 300 km) resolution as orbit altitude is lowered during the end of mission life. This satellite was an excellent source of environmental data useful for analyses of changes in land usage, agriculture, and forest climates.

RapidEye

The RapidEye multispectral pushbroom sensor has five bands at 5 x 5 m spatial resolution, a swath width of 77 km, and a daily revisit time. RapidEye's satellites are the first commercial satellites to offer the red-edge band (690-730 nm), which measures variances in vegetation, allowing for species separation and monitoring vegetation health. The RapidEye constellation of five minisatellites stands apart from other providers of satellite-based geospatial information in their unique ability to acquire high-resolution, large-area image data on a daily basis.

Resourcesat-2

Resourcesat-2 satellites acquire four spectral bands ranging from visible and near-infrared (VNIR) to short-wave infrared (SWIR) wavelengths. The satellite operates in a sun-synchronous orbit at an altitude of 817 km. The satellites take 101.35 minutes to complete one revolution around the Earth and complete about 14 orbits per day. The entire Earth is covered by 341 orbits during a 24-day cycle. Resourcesat carries three scanners: LISS-IV with a 5.8m resolution, the LISS-III with a 23.5m resolution, and AWiFS with a 56 m resolution. Swath width increases from 70 km through 141 km to 740 km for the three instruments, with a 5-day repeat cycle for the AWiFS sensor.

Sentinel-2A and 2B

The Sentinel-2 mission consists of two identical satellites, Sentinel-2A and Sentinel-2B, that were launched using the European VEGA launcher. To achieve frequent revisits and high mission availability, two identical Sentinel-2 satellites (Sentinel-2A and Sentinel-2B) operate together. The satellites are phased 180 degrees from each other in the same orbit. This allows for what would be a 10-day revisit cycle to be completed in 5 days.

SPOT 6, 7

SPOT 6 and 7 collect a panchromatic band with 1.5-meter spatial resolution and four visible-near infrared (VNIR) multispectral bands that support vegetation, geologic, and environmental mapping. The SPOT imagery products offer high resolution over broad areas using the SPOT satellites. An acquisition covers large areas in a single pass at resolutions up to 1.5 meters and with a location accuracy of up to 10 m. Such precise coverage is ideal for applications at regional and local scales from 1:250,000 to 1:15,000. The archive contains imagery acquired since 2012, which is ideal for temporal evolution monitoring. SPOT 6, 7 benefits from a large swath, enabling a daily acquisition capacity of 6 million km². The satellites are specifically designed to efficiently provide large-area coverage, making them particularly suitable to serve cartographic and monitoring applications, ideally for 1:15,000 topographic mapping. All satellites are in sun-synchronous, near-polar orbits at altitudes around 830 km above the Earth, which results in orbit repetition every 26 days.

World View-2and 3

WorldView-2 is the first high-resolution 8-band multispectral commercial satellite. Operating at an altitude of 770 km, WorldView-2 provides 46 cm panchromatic resolution and 1.85-meter multispectral resolution. The WorldView-2 satellite can acquire four side-lapping strips of stereo coverage that measure 112 km by 63 km using its agile pointing capability. WorldView-2 has an average revisit time of 1.1 days and is capable of collecting up to 1 million km2 of 8-band imagery per day, greatly enhancing DigitalGlobe’s multispectral collection capacity for more rapid and reliable collection. These images supply unprecedented detail and geospatial accuracy, further expanding the applications for satellite imagery in both commercial and government markets. Added spectral diversity provides the ability to perform precise change detection and mapping. In addition to numerous other technical improvements, WorldView-2 can accommodate direct tasking, which will allow select customers around the world to load imaging profiles directly up to the spacecraft and execute delivery of the data directly down to their ground stations.

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