Marine environmental monitoring, which is now commonly referred to as ocean observing, has the overall objective of characterizing one or more aspects of the marine water column and its boundaries, in time and the three dimensions of space. It is used for civilian and military purposes and involves a multitude of sensors mounted on five types of platforms – satellites, aircraft, ships, in situ and shore-based installations. Each platform has advantages and disadvantages with the result that oceanographic sensors and other environmental monitoring sensors mounted on these various platforms tend to compliment rather than compete against each other. Collectively, a network of such platforms and sensors is referred to as an ocean observing system.

Earth Observation Satellites

Earth-observing satellites are used in meteorology and oceanography (METOC) and marine operations pertaining to national defence, disaster response, homeland security, offshore oil and gas, marine transportation and coastal mapping. They are also referred to as spaceborne sensors. The military and homeland security sectors are on the vanguard of rapid environmental assessment (REA) in coastal waters, however, the academic community is leading the development of public ocean observing systems.

Successful application requires advanced image analysis techniques to produce satellite imagery and other environmental products, but there is a trend towards producing products in formats that are compatible with common GIS (geographic information system) infrastructure and GIS-based web portals that conform to open standards. In addition to bringing Earth-observation products to the marine community-at-large, this approach is facilitating integration into marine operations and is contributing to the rise of the presently loosely-defined field of operational oceanography.

Which Satellite Sensor Should I Use?

The "Satellite Sensors" side bar on this page leads to five tables that identify satellite sensors used today for coastal and open ocean mapping and monitoring purposes. They are listed according to sensor type and include multispectral, thermal infrared, synthetic aperture radar, altimeter and scatterometer sensors operating respectively in the visible, IR and microwave bands of the electromagnetic spectrum. Presently, there are no spaceborne hyperspectral sensors designed for marine applications, however, hyperspectral sensors mounted on aircraft are used extensively for mapping coastal waters and regions. All of the listed satellites are polar orbiting, which simply means they orbit the poles. This differs from geostationary satellites, which orbit the equator.

If you are not familiar with satellite sensors, then use the "Marine Applications" side bar on this page to identify satellite sensors that are used for a specific purpose. For example, if your application involves coastal mapping or flooding or pertains to water clarity (turbidity) in coastal waters, then the applications side bar will lead you to the land-optimized and marine multispectral satellite sensors. If, on the other hand, you are an oceanographer interested in geostrophic currents and mesoscale processes in the open ocean, the side bar will lead you to various active microwave sensors such as altimeters, synthetic aperture radars and scatterometers. Thermal IR sensors are also used extensively in oceanic environments.

If all this sounds like Greek to you, consultants at OEA Technologies Inc. would be pleased to help you identify your marine environmental monitoring needs. We can also define an effective implementation strategy. Contact Us at your convenience.

Primary Advantages of Satellite Sensors

Earth observation satellites operate covertly, provide wide-area (i.e. synoptic) coverage, deliver both regional and global information and can do so with a single sensor. Other platforms may have some of these operating features, but no other platform has all of them.

Primary Disadvantages of Satellite Sensors

Satellite sensors only observe surface waters and not all types of sensors can be operated from space. Also, the temporal resolution (i.e. how often it samples a given location) of a polar-orbiting satellite is limited – usually on the order of weeks for a single satellite. Temporal resolution can be improved by operating the same sensor on several polar-orbiting satellites (i.e. a constellation) and through advanced sensor design. This can result in an effective revisit time that is considerably shorter than the revisit time of the polar-orbiting satellite itself. Temporal resolution can also be increased dramatically by operating the sensor on a geostationary satellite, however, geostationary sensors tend to have very coarse spatial resolution – on the order of kilometers to tens of kilometers – and they cannot image high-latitude environments.