Optical imagers and multispectral radiometers provide images of Earth's surface and atmosphere. Copernicus Contributing Missions carrying optical imagers complement the multispectral imagery from Sentinel-2 and images from the Ocean Land Colour Instrument and Sea Land Surface Temperature Radiometer to be carried on Sentinel-3.
Optical imagers are amongst the most common instruments used for Earth observation. They are generally nadir-viewing instruments with a horizontal spatial resolution ranging of 1–300 m and swath widths in the order of tens to hundreds of km.
They have many application areas such as agriculture, land-cover mapping, damage assessment associated with natural hazards and urban planning. They are, however, limited to cloud-free conditions and daytime operation.
Measurements may be used to infer a wide range of parameters, including sea- and land-surface temperature, snow and sea-ice cover and cloud cover. They supply an important source of data on processes in the biosphere, providing information on global vegetation and its variation through the seasons – important for identifying areas of drought and early warning of food shortages.
Copernicus Contributing Missions carrying high-resolution imagers and multispectral radiometers include:
Launched in 1995, ERS-2's instrument package included the Along Track Scanning Radiometer (ATSR), which is made up of an infrared radiometer and a microwave sounder. It was used for measuring sea-surface temperatures, cloud-top temperatures and vegetation monitoring with a swath of 500 km and 1×1 km spatial resolution.
Launched in 2002, Envisat was the largest Earth observation satellite ever built. It carried 10 instruments, one of which was the Medium Resolution Imaging Spectrometer (MERIS). With its 15 spectral bands and a ground spatial resolution of 300 m, MERIS achieved global coverage of Earth every three days.
Envisat also carried the Advanced Along-Track Scanning Radiometer (AATSR), with 1 km ground resolution and 500 km swath width. It was designed primarily to measure sea-surface temperature.
This high-resolution Spanish optical mission can see down to a 75 cm ground resolution.
DMC (Disaster Monitoring Constellation) is a network of satellites designed to supply optical multispectral imagery for disaster response and commercial imaging campaigns. It is unique in that each satellite is independently owned and operated by a separate nation. All the satellites have been spaced around a Sun-synchronous orbit to provide daily global imaging capabilities.
The first four satellites, which were launched between 2002 and 2005, have a ground resolution of 32 m and swath widths of about 600 km. A second generation of two satellites (UK-DMC2 and Deimos-1) were launched in 2009 with an increased resolution value of 22 m.
DMC3 is a constellation of three high-resolution optical satellites with
Planned for launch in 2018, EnMAP (Environmental Mapping and Analysis Program) is a German mission to deliver high-quality hyperspectral image data with a swath width of 30 km, spatial resolution of 30×30 m and an off-nadir (30°) pointing feature for fast revisit (4 days).
The mission will offer data on a wide range of ecosystem parameters encompassing agriculture, forestry, soil and geological environments, coastal zones and inland waters.
The HiROS optical satellite system is made up of three satellites. It will offer 0.5 m ground resolution (PAN) and 2 m (MS), and a 12 km swath width. It will have a high revisit time.
The French-Italian Pléiades system is made up of two satellites and is designed to replace the French SPOT missions. The mission has a swath of 20×20 km and ground resolution of 50 cm. Pléiades complements the Italian radar satellite constellation Cosmo-SkyMed.
Prisma is an Earth observation system with innovative electro-optical instrumentation that combines a hyperspectral sensor with a panchromatic, medium-resolution camera. It has a spatial resolution of 20–30 m (hyperspectral) and 2.5–5m (PAN), and a swath width of 30–60 km.
ESA's Proba-V is a small satellite mission to follow-on from the Vegetation instrument on the SPOT satellites. It was launched in May 2013 and has a 300 m ground resolution and 2250 km swath width. It offers better signal to noise resolution, and higher accuracy with respect to the instruments on board the SPOT satellites.
The German RapidEye fleet of five satellites, each about the size of a fridge, was launched in 2008. The multispectral imager onboard each spacecraft images Earth in five spectral bands, scanning a 77 km swath at 6.5 m resolution and each strip with a maximum length of 1500 km.
The constellation is designed to provide insurance and food companies, farmers, governments, other agencies and institutions throughout the world with up-to-date customised information products and services.
Spain's SEOSat-Ingenio is a SPOT-class observation satellite with 2.5 m PAN and 10 m MS resolution. It has a 60 km swath in MS and 30 km in PAN. It is scheduled for launch in 2015.
The French SPOT series of optical satellites began imaging the Earth in 1986. The latest in the series, SPOT-5, was launched in 2002. With a ground resolution of 2.5–5 m in PAN and 10 m in MS and with a swath of 60×60 km (and 60×120 km in twin-instrument mode), SPOT-5 provides an ideal balance between high-resolution and wide-area coverage.
VENµS is the first cooperation between Israel and France for the Earth observation using a superspectral sensor. It is planned to be operational in 2016 and is dedicated to monitoring vegetation. It will acquire high resolution and superspectral images of predefined sites of interest all around the world.