Universe Today

Image credit: NASA

NASA satellites have been watching a gigantic iceberg as it disrupts the fragile Antarctic marine environment. The iceberg, named C-19, is 32 km wide and 200 km long; it broke off the Ross Ice Shelf back in May 2002. The problem is that the iceberg stopped winter sea ice from moving out of the Ross Sea region. Phytoplankton, which needs sunlight, was reduced by 90%, and so the rest of the ecosystem suffered too. The iceberg is being watched with NASA’s Terra and OrbView2 satellites.

NASA satellites observed the calving, or breaking off, of one of the largest icebergs ever recorded, named “C-19.”

C-19 separated from the western face of the Ross Ice Shelf in Antarctica in May 2002, splashed into the Ross Sea, and virtually eliminated a valuable food source for marine life. The event was unusual, because it was the second-largest iceberg to calve in the region in 26 months.

Over the last year, the path of C-19 inhibited the growth of minute, free-floating aquatic plants called phytoplankton during the iceberg’s temporary stopover near Pennell Bank, Antarctica. C-19 is located along the Antarctic coast and has diminished little in size. Since phytoplankton is at the base of the food chain, C-19 affects the food source of higher-level marine plants and animals.

Kevin R. Arrigo and Gert L. van Dijken of Stanford University, Stanford, Calif., used chlorophyll data from NASA’s Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The instrument, on the OrbView-2 satellite, also known as SeaStar, was used to locate and quantify the effects of C-19 on phytoplankton. The researchers were able to pinpoint iceberg positions by using images from the Moderate Resolution Imaging Spectroradiometer (MODIS), an instrument aboard NASA’s Terra and Aqua satellites. The findings from this NASA-funded study appeared in a recent issue of the American Geophysical Union’s Geophysical Research Letters.

C-19 is about twice the size of Rhode Island. When it broke off the Ross Ice Shelf, the iceberg was 32 km (almost 20 miles) wide and 200 km (124 miles) long. It was not as large as the B-15 iceberg that broke off of the same ice shelf in 2001 but among the largest icebergs ever recorded.

Since it was so large, C-19 blocked sea ice from moving out of the southwestern Ross Sea region. The blockage resulted in unusually high sea-ice cover during the spring and summer. Consequently, light was blocked. Phytoplankton blooms that occur on the ocean surface were dramatically diminished, and primary production was reduced by over 90 percent, relative to normal years.

Primary production is the formation of new plant matter by microscopic plants through photosynthesis. Phytoplankton is at the base of the food chain. If they are not able to accomplish photosynthesis, all organisms above them in the food chain will be affected. “Calving events over the last two decades indicate reduced primary productivity may be a typical consequence of large icebergs that drift through the southwestern Ross Sea during spring and summer,” Arrigo said.

Arrigo and van Dijken also used imagery from the Defense Meteorological Satellite Program (DMSP) satellite Special Sensor Microwave Imager and Scanning Multichannel Microwave Radiometer, managed by the U.S. Department of Defense. The data was used to monitor the impact of C-19 on the movement of sea ice. The data is archived at the National Snow and Ice Data Center, University of Colorado, Boulder.

Arrigo said most of the face of the Ross Ice Shelf has already calved. There is another large crack, but it is very difficult to predict if and when another large iceberg will result.

NASA’s Earth Science Enterprise is dedicated to understanding the Earth as an integrated system and applying Earth System Science to improve prediction of climate, weather, and natural hazards using the unique vantage point of space.

Original Source: NASA News Release

Image credit: ESA

The European Space Agency’s demonstrated the capability of its Envisat Earth monitoring satellite to track the water levels of inland lakes and rivers; spots on the Earth that were previously invisible to previous radar altimetry. The Radar Altimeter 2 on board Envisat sends 1800 radar pulses a second from 800 km altitude and then calculates how long they take to return – this tells the device its exact distance to the planet. A team from pored through the raw Envisat data and figured out a way to extract river water levels by spotting specific kinds of radar echos. ESA will release 12 years of river levels for scientists to study.

For over a decade ESA has used satellites to bounce radar pulses off the Earth and precisely measure the height of ocean and land surfaces. But inland lakes and rivers have been effective blind spots for radar altimetry ? at least until now.

Next week ESA previews a new product range called River and Lake Level from Altimetry that provides previously inaccessible information on water levels of major lakes and rivers across the Earth’s surface, derived from Envisat and ERS radar altimeter measurements.

Hydrologists can use this new data to monitor river heights around the planet, assess the impact of global warming and help with water resource management. Inland water bodies are important as key sources of both water and food for the people living round them. They are also often regions of maximum biodiversity and represent early indicators of regional climate change.

A new processing algorithm has been developed to extract rivers and lakes level findings from raw radar altimeter data. The development effort was headed by Professor Philippa Berry of the UK’s De Montfort University: “The new radar altimeter product is a great leap forward for hydrologists. It gives them a new tool to study both the historical changes in water table levels and critically important data to use in forecasting models of water availability, hydroelectric power production, flood and drought events and overall climate changes.”

The Radar Altimeter 2 (RA-2) flown aboard ESA’s Envisat environmental satellite is the improved follow-on to earlier radar altimeters on the ERS-1 and ERS-2 spacecraft. From its 800 km-high polar orbit it sends 1800 separate radar pulses down to Earth per second then records how long their echoes take to return ? timing their journey down to under a nanosecond to calculate the exact distance to the planet below.

Radar altimeters were first flown in space back in the 1970s, aboard NASA’s Skylab and Seasat. These early efforts stayed focused firmly on the oceans, as less-smooth land surfaces returned indecipherable signals. But as the technology improved reliable land height data became available. Envisat’s RA-2 has an innovative ‘four-wheel drive’ tracking system allowing it to maintain radar contract even as the terrain below shifts from ocean to ice or dry land.

But rivers and lakes have proved tougher targets. Large lakes and wide rivers such as the Amazon often returned tantalising ‘wet’ radar signals, but echoes from nearby dry land distorted most such signals.

Believing full-fledged river and lake level monitoring was nevertheless feasible, ESA awarded a contract to De Montfort University to develop a suitable software product, with Lancaster University advising on field hydrology.

The De Montfort University team proceeded by painstakingly combing through many gigabytes of raw data acquired over rivers and lakes, taking note of the type of echo shapes that occurred. They sorted different echo shapes into distinct categories, then created an automated process to recognise these shapes within ‘wet’ signals and eventually extract usable data from them.

“To do this, the shape of each individual echo has to be analysed, and the exact time corresponding to the echo component from the lake or river must be calculated,” explained Professor Berry. “As well as identifying and removing the echo from surrounding land, this process is complicated by the frequent occurrence of islands and sandbars, particularly in river systems. But in the end this approach has been shown to be very effective indeed, with successful retrieval of heights from the majority of the Earth’s major river and lake systems.”

Next week sees the release of the first demonstration products using this new algorithm, containing representative data from the last seven years for rivers and lakes across Africa and South America. The plan is that global altimeter data for the last 12 years will then be reprocessed to provide hydrologists with historical information, invaluable for assessing long-term trends.

ESA also intends to install operational software in its ground segment so eventually the product can be delivered to users in near-real time, within three hours or less of its acquisition from space.

Hydrologists need no previous knowledge of radar altimetry to make use of the new data, with one product known as River Lake Hydrology providing data corresponding to river crossing points, just as though there were actual river gauges in place.

Such gauges are the traditional way that river and lake level measurements are obtained, but their number in-situ has declined sharply in the last two decades. The new product will compensate for this growing lack of ground data.

The other product is called River Lake Altimetry, intended for altimetry specialists, and provides all crossing points for a water body, together with detailed information on all instrumental and geophysical corrections.

Previews of both products can be accessed via a dedicated website (see right hand bar) or on a free CD ? email [email protected] to order a copy. Both products are being formally announced at the Hydrology from Space conference, beginning Monday 29 September in Toulouse.

Original Source: ESA news release