ScienceDaily (Dec. 5, 2008) — Based on the outstanding success of the first tandem mission between ERS-2 and Envisat last year, ESA has paired the two satellites together again to help improve our understanding of the planet.
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.WEATHER NOTE
StormZone Simulation 2008
The Miami-Dade County Department of Emergency Management & Homeland Security (DEM&HS) recently hosted approximately 60 students and teachers from South Dade Senior High School in Homestead and Eugenia E. Thomas Middle School in Doral to participate in a simulated activation of the County's Emergency Operations Center (EOC).
The students, who are involved in a magnet program to study emergency management, role-played elected officials, emergency management coordinators and other key personnel during a fictional Category 3 hurricane that struck Miami-Dade. Three DEM&HS coordinators assisted the students during the exercise. The simulation was coordinated by StormZone, a Miami-based non-profit organization that teaches emergency management to middle and high school students.
A series of heavy rain events, partially caused by the remnants of three tropical storms, produced serious and widespread flooding across northern Illinois and northwest Indiana in September.
The first heavy rain occurred on September 4 and 5 when remnants of hurricane Gustav brought two to four inches of rain to the region. Because of dry conditions through much of August, this rain didn’t cause any significant flooding. However, it saturated the ground, increased flows on area streams, and set the stage for more serious flooding later in the month. Moisture from a Pacific tropical storm, Lowell, moved along a stationary front producing a wave of heavy rain across northern Illinois and northwest Indiana on the 13th.
This was followed by a second wave of heavy rain on the 14th, as the remnants of Hurricane Ike moved up from Texas. Rainfall totals on September 13 and 14 were 7 to 11 inches, with the heaviest totals in Lake and Porter Counties in northwest Indiana. The total September rainfall for the area was 12 to 16 inches.
The image shows rainfall across the entire Midwest from September 12-15, 2008. This image is courtesy the Midwestern Regional Climate Center in Champaign, IL.
The result of the heavy rain was widespread flooding of roads, creeks, drainage areas, open fields, low lying areas and basements. Small streams such as the North Branch of the Chicago River, Salt Creek, the DuPage River, the Little Calumet River and its tributaries rapidly rose to record or near record levels. These small streams fed larger rivers including the Des Plaines, Fox, Kankakee, and Illinois Rivers. The Des Plaines reached the second highest crest on record at Des Plaines and Riverside, while the Illinois set records at Morris and LaSalle.
Flooding in downtown Des Plaines. Photo courtesy of CLTV.
Flooding at O'Hare International Airport.
Despite two significant tornado outbreaks, on January 7 and June 7, and an intense wind and tornado event on August 4, the flooding of mid September was by far the biggest weather event in the Chicago area for 2008. This event impacted more people and resulted in more damage and fatalities than any event in this area in the last several years. Total estimated damages from the flooding are around 100 million dollars. There were four flood related fatalities, making this the most deadly storm-related weather event in northern Illinois and northwest Indiana since eight people were killed by a tornado in Utica in April, 2004.
Flooding on the Illinois River at Peru.
Historically, about half of all flood fatalities occur in vehicles, when people drive into flooded roads, or get swept off a road by fast moving water. While there were several incidents where people in vehicles were swept away by flood water and had to be rescued, none of the four fatalities in the September flooding occurred in vehicles. Hundreds of cars were also stranded in deep standing water, fortunately with no loss of life. Here is a review of the four fatalities;
Record flooding along the Illinois River at Morris. Photo by Don Lyon.
Have a happy and SAFE holiday season, and rest assured that the men and women at your National Weather Service office in Romeoville are on guard 24/7, watching out for you.
The National Weather Service office in Romeoville has completed the StormData summary of the September flooding in northern Illinois and northwest Indiana. StormData is a monthly publication that documents all hazardous weather occurrences. It is available online at http://www.crh.noaa.gov/lot/?n=stormdata.
Travelling is always a fun experience as you get to explore a lot of new destinations and take part in various activities. In fact there is countless number of people on the surface of the earth who consider travelling to be their favourite hobby and go out exploring new places whenever they get time. There are some other people who need to travel a lot not because they are fond of it but they have some professional requirements.
Travelling with family or for education are other two important reasons why people do travel extensively. Whatever be the reason for your travel, you need to extremely careful about the safety while you are not at the home town. The foreign places can at times be very risky. Accidents, robberies and disease are the reasons why you need to take adequate safety measures while travelling.
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They do not carry adequate number of oxygen masks, life jackets and life belts. This is the reason why at the time of any emergency they are not able to help you out. In fact you need to be careful about your health conditions as any negligence can take your life. If you feel that as you are travelling by a ship or a train, you do not need to take care of the travel safety arrangements than you are quite wrong. Because accidents can take place anytime and anywhere.
There are other safety measures that you need to take in order to make sure that you travel safely. If you are going for international tours then never forget to fetch enough information about the rules and restrictions of that country. This will help you to keep away from many unwanted troubles. If this is the first time you are visiting the place then a travel agency can be of help to you.
Always make sure that you have a travel insurance that will cover all sorts of medical expenses abroad. You should be extremely careful about the identity documents you are carrying like the passport and visa loosing which can land you up in jail as this is a criminal offence to intrude into a foreign country without official proof. So be conscious about your safety while going for a tour.