e d u s p a c e

Remote Sensing Principles | Resource Satellites

	Resource Satellites [ ]
	Introduction
	LANDSAT
	SPOT
	ERS
	ENVISAT
	RESURS
	IKONOS
	QUICKBIRD
	Introduction
	Weather satellites are designed to measure atmospheric conditions, whilst resource satellites are designed for mapping surface conditions on the Earth. A key difference between weather and resource satellites is that weather satellites must acquire frequent images of large areas whereas resource satellites must acquire high resolution images in a range of spectra. The high resolution required necessitates smaller scanning areas and, therefore, more limited area coverage, which in turn means that it takes several days to scan the entire Earth. So a particular point on the Earth's surface can only be scanned once every few days. On the other hand, since the high spatial resolution makes it possible to distinguish small detail, it is possible to map in greater detail. The high spectral resolution resource satellites can detect a greater range of radiation levels. This is exploited in area mapping as it is possible to differentiate the spectral profiles of various surfaces.
	LANDSAT
Source: Government Raster Image Processing Software and Data 2, Meridian Data, inc.	The Hubbard Glacier in south-eastern Alaska seen from LANDSAT. In 1986 it pushed forward and dammed the Russell Fjord south east of the glacier, producing an ice lake. The picture is a processed image from LANDSAT channels 2, 3 and 4. So far, the LANDSAT series has produced six satellites. The first three were equipped with multispectral scanners (MMS) with a spatial resolution of 80 metres and a spectral resolution of 4 channels in the visible and near infrared ranges. LANDSAT 4 and 5 are in addition equipped with a Thematic Mapper (TM), which has seven channels including one thermal infrared band. The spatial resolution is 30 metres - this means that each pixel represents an area on the Earth's surface 30 metres by 30 metres. See also a radar image of the same glacier.
False colour composite image based on LANDSAT data in the near infrared, red and green channel. Green vegetation is seen as shades of red. Settlement and bare soil areas are seen as bluish.	Landsat's high spectral resolution ensures that they are currently the best sensors for area classification and they have made an important contribution to the development of the field. They are equipped with three channels in the visible spectrum (blue, green and red) and three channels in the near infrared spectrum where the atmosphere is most translucent. See the different channels here. The tecnical specifications of LANDSAT are found here.
	SPOT
Stereoscopic sensing by SPOT is used in elevation calculations.	The French Systeme Probatoire d'Observation de la Terre includes the so-called SPOT satellite. It was launched on February 21st 1986. It can sense in three spectral bands (green, red and the near infrared) with a resolution of 20 metres. Furthermore, it is equipped with a panchromatic scanner, which means that it scans within a band which includes the green and red ranges of visible light. The spatial resolution for this sensor is 10 metres, for many years the highest resolution for a non-military sensor.
See example	SPOT has a special feature that it can be programmed to "look sideways" and scan the same strip twice under two consecutive overpasses. The two different visual angles on the same area give a stereoscopic effect, which makes it possible to map elevation conditions. As SPOT has two visual and one near infrared channel it is ideally suited for vegetation mapping of small local areas. The tecnical specifications of SPOT are seen here.
	ERS
	Under the management of the European Space Agency, ESA, the satellites ERS-1 and ERS-2 have been built by the European industry. The satellites were launched in 1991 and 1995 respectively. They are equipped with an active microwave system that can acquire data through thick cloud cover and during the night. One of the instruments, the Scatterometer measures the wind direction and speed over the oceans; another sensor, the Altimeter can measure wave height. However perhaps the best known sensor, the Synthetic Aperture Radar (SAR) images the surface and its data can be used for mapping. However the interpretation of a SAR image is very different from that acquired from an optical or infrared sensor. SAR images do not show colours but provide information linked to the surface roughness. For a SAR sensor, a sea surface with medium to high waves caused by wind is an example of a rough surface; whilst a calm sea or one with only very small waves is a smooth surface. On the land, a forest is a rough surface and will appear bright, while grassland or a highway would appear very dark, as they represent a relative smooth surface for the radar.
The image shows the Gaeta Bay on the west coast of Italy. The volcano of Roccamonfina is seen to the right. Due to the oblique illumination of the radar beam the morphology of the landscape is very much enhanced. The different tones of grey in the sea surface are due to local differences in the wind regime roughening the water in some places more than in others, typical of low wind speed weather conditions.	The mapping and monitoring of sea ice advance/retreat in arctic waters has become possible thanks to the all-weather radar sensor. It is important to assist the study of global climatology, as changes in sea ice area reflect changes in temperature and sea currents. Another important global ecological issue is monitoring deforestation of the tropical rainforest. Radar sensors can detect forest clearings despite the cloudy weather of the tropics. An ATSR (Along-Track Scanning Radiometer) scanner has been installed on the ERS2. It is a traditional passive scanner with 7 channels in the visible, near infrared and thermal infrared ranges. The thermal infrared channel is especially useful for sea surface temperature mapping. The visible and near infrared channels may be used for global mapping of vegetation with a spatial resolution of 1km. ERS2 is also equipped for global mapping of the ozone layer. Data from ERS2 may play a vital part in scientific understanding of the variations of the ozone layer and in the assessment of the part played by man-made pollution. More information on radar technology. The tecnical specifications of ERS 1 and ERS 2 are found here.
	ENVISAT
	On the 1^st March 2002, the European Space Agency launched ENVISAT, an advanced polar-orbiting Earth Observation satellite which provides measurements of the atmosphere, ocean, land and ice over at least the next five years. ENVISAT data will support Earth science research and enable monitoring of environmental and climatic changes. Furthermore, its data will facilitate development of operational and commercial applications.
The ASAR image covers the Antarctic Peninsula, which extends for 1000 km south to north and is situated between the Bellingshausen Sea to the west and the Weddell Sea to the east. This is a region that has experienced exceptional atmospheric warming since the 1950s and is therefore of key interest for global change research. Over the last 50 years an average temperature increase of 2.5°C has been observed at the climate stations on the Peninsula. This has triggered the retreat and break-up of several ice shelves, culminating in the collapse of the two northern parts of the Larsen Ice Shelf in January 1995 (Larsen A) and in March 2002 (Larsen B). The launch of Envisat on 1 March 2002 occurred just in time to capture the dramatic break-up of Larsen B.	The Advanced Along Track Scanning Radiometer (AATSR) establishes continuity of the ATSR-1 and ATSR-2 datasets (from the ERS series) for precise sea surface temperature (0.3K or better) measurements to assist climate research and for operational and scientific users. An Advanced Synthetic Aperture Radar (ASAR), operating at C-band, ensures continuity of data after ERS-2. It features enhanced capability in terms of coverage, range of incidence angles, polarisation, and modes of operation. The improvements allow radar beam elevation steerage and the selection of different swaths, 100 or 400km wide.
The first MERIS observation captured a huge phytoplankton patch produced by an "upwelling" mechanism along the Mauritanian coast. The unprecedented resolution allows fine scale structures to be detected. In such upwelling areas north-east trade winds bring deep and nutrient-rich water to the surface, feeding phytoplankton. Changes in climate affect the intensity of the upwelling with important consequences for marine ecosystems, fisheries and the local economy.	MERIS is a imaging spectrometer that measures the solar radiation reflected by the Earth, at a ground spatial resolution of 300m, with 15 spectral bands in visible and near infra-red and programmable in width and position. MERIS allows global coverage of the Earth every 3 days. The primary mission of MERIS is the measurement of sea colour in oceans and coastal areas. Knowledge of sea colour can be converted into a measurement of chlorophyll pigment concentration, suspended sediment concentration and aerosol loads over marine areas, all of which are import to the study of ocean carbon cycle and upper ocean thermal regime. The data will also be used for management of fisheries and coastal zones. In order to understand the processes which determine the physical and the photochemical behavior of the atmosphere, detailed global measurements of the amount and horizontal and vertical distribution of ozone in addition to many other atmospheric trace-gases is necessary. Onboard ENVISAT the following sensors provide relevant data: The Global Ozone Monitoring by Occultation of Stars (GOMOS) The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) The SCanning Imaging Absorption SpectroMeter for Atmospheric ChartographY (SCIAMACHY) The tecnical specifications of Envisat are found here. More information about Envisat can be found on its dedicated website at: www.esa.int/envisat/
	RESURS
A section of an image from RESURS on August 12th 1995, showing an area in north-western Jutland, Denmark. Hjarbaek Fjord is seen in the middle. The image was put together on the basis of one near infrared channel, shown in red and two visible channels, shown in green and blue colours. The intensity of the red colour therefore reveals the level of photosynthetic activity. It can be seen that low-lying areas e.g. hollows along water streams are characterized by green grass (very red), while agricultural areas are less red, as the grain crops are ripe at this time of year and photosynthesis less active. Forest and other uncultivated areas are dark. Water surfaces are the darkest. The pixel size (resolution) in the image is 160m.	The Soviet Union and later Russia developed the RESURS satellites, which have been in orbit since 1985. They are equipped with scanners with four channels in the visible and near infrared ranges and one thermal infrared channel. Since the RESURS satellite has a large area coverage scanning a strip which is 600km wide, the same areas are scanned at brief intervals (eg 4 days at the Equator and 2 or 3 days in Europe). At the same time the sensor has a spatial resolution of 160m so that it may be used in the detailed mapping of large areas. RESURS fills a gap in the capabilities of similar sensors in that the NOAA satellite covers large areas, but has a limited range of detail (a resolution of 1km) and the LANDSAT and SPOT satellites, which both have limited area coverage, but high spatial resolution (10, 20, 30m resolution). So RESURS is a very important sensor for creating regional surveys, with LANDSAT and SPOT data providing high detail over smaller key areas and NOAA providing an overview of larger areas which may include mapping issues such as forest clearance, desertification, agricultural growth, snow and ice extent, floods and forest fires at scales of 1:500,000 and 1:1.000,000.
	IKONOS
Part of Coloseum, Rome, seen from Ikonos at 680km altitude.	The IKONOS satellite can differentiate objects less than one metre square on the ground - enough to distinguish between a car and a truck. This capability from an orbital altitude of 680 km represents a significant increase in image resolution over any other commercial remote sensing satellite system before it. The Optical Telescope Assembly captures the imagery across an 11 to 13km swath of the Earth's surface, and reflects it to the digital imaging sensors. Images from IKONOS are some of the most detailed satellite images available for non-military use. It also carries a 4 metre resolution multispectral sensor with 3 visible channels and one near-infrared similar to Landsat 4 and 5 making detailed land use mapping possible. The technical specifications of IKONOS are found here.
	QUICKBIRD
	QuickBird was launched from Vandenberg Air Force Base in California October 18, 2001. QuickBird's launch resulted in the highest resolution commercial satellite in operation.
This is a 2.44 metre false colour (bands 4, 3, and 2) multispectral image of the Miyake-jima volcano, collected by QuickBird on March 14, 2002; the false colour band combination reveals the sharp contrast between the vegetated and non-vegetated regions on the volcano, caused by recurring lava flows. Situated about 200 kilometres south-southwest of Tokyo, the circular island of Miyake-jima rises about 1100 metres from the sea floor, and spans approximately 8 kilometres in diameter at sea level. The eruption of 2000 is still ongoing as of April 2002, and all inhabitants have been evacuated since September 2000. Image courtesy of DigitalGlobe	QuickBird circles the globe 600km (about 372 miles) above Earth while the QuickBird sensor (a high resolution camera) gathers images of the Earth's surface during daylight hours. The system collects 61 centimetre panchromatic and 2.5 metre multispectral stereoscopic data. QuickBird is designed to efficiently and accurately cover large areas with great accuracy. The QuickBird spacecraft is capable of acquiring over 75 million square kilometres of imagery data annually (over three times the size of North America). The data will contribute to mapping, agricultural and urban planning, weather research and military surveillance. The tecnical specifications of QuickBird are found here.