ERS-2, ESA’s veteran spacecraft, and Envisat, the largest environmental satellite ever built, both carry Synthetic Aperture Radar (SAR) instruments that provide high resolution images of the Earth's surface.
By combining two or more SAR images of the same site, slight alterations that may have occurred between acquisitions can be detected. This technique, known as SAR interferometry or InSAR, has proven to be very useful for applications such as glacier monitoring, surface deformation detection and terrain mapping.
ESA engineers configured the first SAR tandem mission, which took place from September 2007 to February 2008, and the current one, which began on 23 November, to ensure that the satellites both acquire data over the same area just 28 minutes apart.
This short time separation allows for changes that occur quickly to be detected. Fast-moving glaciers, for instance, move more than 200 m per year and can move as much as 1 cm in 30 minutes. The ability to detect these small changes occurring on the ground between acquisitions is also allowing scientists to understand better and improve the quality of the SAR interferometry technique.
The current tandem mission, scheduled to run until 27 January 2009, is continuing the work of the first tandem mission with respect to measuring the velocity of fast-moving glaciers, detecting land-ice motion and developing elevation models over flat terrain.
However, based on the first mission’s proven ability to provide precise elevation information over flat regions, data from the current mission will also be used to identify natural carbon sources and sinks in Kazakh Steppe and wetlands in permafrost regions.
A challenging configuration
ESA engineers had to overcome many challenges in order to put Envisat and ERS-2 into a tandem flight configuration. For instance, in 2001 ERS-2 lost the ability to be manoeuvred in the usual way by onboard gyroscopes, navigational tools that allow mission controllers to maintain the correct position of satellites.
The operational lifetime of satellite missions is normally determined by the functioning of onboard gyroscopes. Without them, the ESA team had to work out a way of positioning the spacecraft by operating onboard sensors in a new way.
Part of their creative solution involved using a device called the Digital Earth Sensor (DES), which is designed to provide the horizon line to allow basic checks on the spacecraft’s position, and analysing Doppler frequency shifts in the signals of ERS-2’s radar instruments.
ERS-2, launched in 1995, and Envisat, launched in 2002, have exceeded the time they were intended to stay in orbit. Since they remain operational and continue to provide quality data about our planet, engineers are trying to use as little fuel as possible so as not to shorten their lifetimes.
"The strategy is to align the tandem start date with an Envisat manoeuvre. Therefore, there is no need to spend extra hydrazine for Envisat. For ERS, the manoeuvre to place it in tandem position is such that the satellite drifts back to its nominal orbit without additional manoeuvre after the tandem campaign," ESA Mission Planner Manager Sergio Vazzana said.
Mariangela D'Acunto | alfa
MSU astronomers discovered supermassive black hole in an ultracompact dwarf galaxy
14.08.2018 | Lomonosov Moscow State University
ASU astrophysicist helps discover that ultrahot planets have starlike atmospheres
13.08.2018 | Arizona State University
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur
What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...
The quality of materials often depends on the manufacturing process. In casting and welding, for example, the rate at which melts solidify and the resulting microstructure of the alloy is important. With metallic foams as well, it depends on exactly how the foaming process takes place. To understand these processes fully requires fast sensing capability. The fastest 3D tomographic images to date have now been achieved at the BESSY II X-ray source operated by the Helmholtz-Zentrum Berlin.
Dr. Francisco Garcia-Moreno and his team have designed a turntable that rotates ultra-stably about its axis at a constant rotational speed. This really depends...
08.08.2018 | Event News
27.07.2018 | Event News
25.07.2018 | Event News
14.08.2018 | Life Sciences
14.08.2018 | Life Sciences
14.08.2018 | Earth Sciences