Remote sensing data
THE CASPIAN BOX
The Caspian Sea has a promising future for oil & gas production growth. The littoral states (Azerbaijan, Russian Federation, Kazakhstan, Turkmenistan, Iran) use the Caspian sea to extract and transport oil & gas. Therefore, the pressures and threats on the ecologically rich ecosystem of the Caspian Sea will continue to be high in the future.
Image source(right): Wood Mackenzie
OBSERVING CASPIAN SEA FROM THE SPACE
Remote sensing is observing and acquiring data about an object without touching it. The sensor is usually located on a satellite platform which ensures global coverage and revisiting capabilities of the same site. Remote sensing complements and even enhances traditional in situ surveys, which are needed for calibration/validation. Some of the applications of satellite remote sensing can be as simple as measuring the temperature of the sea surface. Other applications are an indirect product of what the sensor measured as seeing the colour of the sea surface to derive a chlorophyll-a concentration.
BENEFITS FOR THE CASPIAN SEA
The Caspian Sea may greatly benefit from satellite remote sensing. Given the difficulties deriving from the uncertainty of the actual legal status of the Caspian Sea, satellite remote sensing has the unique capability of collecting data everywhere and even capturing a synoptic (or quasi) view of the whole basin. Satellite remote sensing can be also seen as a mean of enhancing cooperation and integration between littoral states as well as an important source of information to support a sound marine and maritime policy in the Caspian Sea.
There are a large number of (optical and radar) sensors, and each one supplies data at different spatial and temporal resolutions. Representative examples are selected taking into account the following guidelines: (1) open access to raw data; (2) processing is mature and not complex; (3) calibration/validation possible; (4) meeting needs of a wide user base (i.e. not only scientific organizations); (5) output clear and simple (e.g., map is a picture that the "eyes" of anybody can understand); (6) looking at CASPINFO service (in situ data a valuable asset for calibration/validation).
Sea Surface Temperature (SST) is the thermometer of the sea surface skin. The current archive contains data from 14 satellites (e.g. AVHRR unique record back 1981) and long-term availability is guaranteed. SST is key input parameter to help : (1) oceanographers study ocean dynamics; (2) meteorologists predict weather and climate; (3) fishermen locate fishing areas; 4) policy makers decide marine spatial planning. As an example, a snapshot of SST from MODIS sensor aboard Terra satellite is provided. The image provides insight to mesoscale variability (e.g. fronts, upwelling, etc.) at local scale but also a consistent view of the whole sea (e.g. warmer/colder regions).
Ocean Colour (OC) is the indicator of substances and organisms within it. The archive contains data from various satellites (since 1978 with CZCS). The ESA (Meris) and NASA (MODIS) missions ensure that observations are not broken and a continued record in the future would be ensured. OC is a key input parameter to help: (1) oceanographers study ocean health oil; (2) companies assess environmental impacts; (3) fishermen locate fishing areas; (4) policy makers manage natural living-resources. As an example, a snapshot of chlorophyll concentration derived from OC observations of MODIS sensor aboard Aqua satellite is provided. The image shows where there are high and low concentrations of chlorophyll. This gives an idea of how many organisms are present.
Sea Level Altimetry
Sea level in the Caspian Sea is a topic of growing concern to all five surrounding countries (Azerbaijan, Republic of Iran, Kazakhstan, Russian Federation and Turkmenistan). The Caspian Sea is subject to significant water level fluctuations which have had serious consequences for low-lying and densed-populated coastal areas, displacing thousands of people, destroying investments in industry and infrastructure and causing severe pollution threats via inundation of near shore waste sites.
The figure shows the sea level variability from the longest record measured at Baku (since 1837). There is a clear evidence of a rising of more than 2 metres between 1977 and 1995. The sea level is now stabilized near the -27 m level. Understanding its variability at all scales is a complicated puzzle being the result of a combination of several factors such as climatic (atmospheric variations), anthropogenic (e.g., river drainage and water use, especially Volga), geologic (e.g. subsidence).
Radar altimetry is an important technique for sensing sea level from space. It is just a more complicated tide gauge with the difference that the altimeter-derived measurements are an average over a footprint with much lower revisiting time. The raw data provided by the altimeters do not come ready for use. A complex sequence of processing steps is still necessary to transform these raw data into usable sea level information. These steps essentially consist of removing unwanted effects caused by the instrument, atmosphere and ocean Thanks to continuous system improvements, radar altimetry is now capable of monitoring the open sea surface at cm accuracy.
Radar altimetry faces some technical challenges in small water bodies. The main reason is that past altimeters were designed for open ocean operation. The re-analysis and improvement of the existing data sets makes now possible to better use altimeter data in those regions. A new class of altimeters (e.g., ALTIKA, Sentinel-3, SWOT, etc.) even promises better regional capabilities. Vignudelli et al. (2011) provides an in depth review of the topic.
Figure shows the basin scale sea level variability derived using altimeter data from TOPEX/Poseidon, Jason, Envisat and GFO satellite missions during the. The Caspian Sea level exhibits clear seasonal signal, probably due to climatological (evaporation & precipitation) and hydrological (river runoff, discharge to Kara Bogaz Gol) cycle. Inter-annual tendencies might be interpreted in the light of decadal climate variability and amplification of irrigation in the Volga river basin
Directly or indirectly altimetry can help in fishery planning, ship routing, offshore operations but more importantly can contribute to the early-detection of rising or falling sea level.
Reference: Vignudelli S., Kostianoy A. G., Cipollini P., Benveniste J. (Editors), Coastal Altimetry, Springer-Verlag Berlin Heidelberg, doi:10.1007/978-3-642-12796-0, 578 pp, 2011.