19. July 2017

DLR sup­plies pre­ci­sion transpon­ders to the Cana­di­an Space Agen­cy

DLR pre­ci­sion transpon­der in Mon­tréal, Cana­da
Image 1/5, Credit: DLR (CC-BY 3.0).

DLR precision transponder in Montréal, Canada

A DLR pre­ci­sion transpon­der on the grounds of the Cana­di­an Space Agen­cy (CSA) in Mon­tréal, Cana­da; the transpon­der is ini­tialised and aligned by re­mote con­trol. Af­ter over­flights, the cap­tured radar sig­nals and mea­sure­ment da­ta are saved and down­load­ed. DLR has the ca­pa­bil­i­ty to ac­cess the transpon­ders from Oberp­faf­fen­hofen.
Sen­tinel-1A radar im­age of Mon­tréal
Image 2/5, Credit: DLR (CC-BY 3.0).

Sentinel-1A radar image of Montréal

A Sen­tinel-1A SAR im­age of Mon­tréal, with the two DLR pre­ci­sion transpon­ders. The first test over­flights with Sen­tinel-1 were per­formed af­ter suc­cess­ful in­stal­la­tion and com­mis­sion­ing of the transpon­ders on and close to the CSA com­plex. The transpon­ders ap­pear as bright crosshairs and are eas­i­ly dis­tin­guish­able from the im­age back­ground. Known as im­pulse re­spons­es, they are shown again in an en­larged form in the box at the bot­tom right. The re­flec­tion from the CSA build­ing is clear­ly vis­i­ble in the vicin­i­ty of the low­er im­pulse re­sponse.
DLR pre­ci­sion transpon­der for the CSA Radarsat con­stel­la­tion mis­sion
Image 3/5, Credit: DLR (CC-BY 3.0).

DLR precision transponder for the CSA Radarsat constellation mission

A DLR pre­ci­sion transpon­der for the Cana­di­an Space Agen­cy (CSA) Radarsat Con­stel­la­tion Mis­sion. The transpon­der unit with its trans­mit­ting and re­ceiv­ing an­ten­nas is vis­i­ble at the top right of the im­age; both an­ten­nas are en­closed in a hous­ing to pro­tect them from var­i­ous en­vi­ron­men­tal fac­tors like wind and rain. The du­al-ax­is ro­ta­tion sys­tem, used to align the transpon­der with the satel­lite dur­ing over­flights is lo­cat­ed be­low this. The con­trol unit is on the left; it is used for re­mote align­ment of the transpon­der and to record the re­ceived sig­nals and mea­sure­ment da­ta.
Sentinel-1 satellite
Sen­tinel-1 satel­lite
Image 4/5, Credit: DLR (CC BY-NC-ND 3.0)

Sentinel-1 satellite

The Eu­ro­pean Space Agen­cy (ESA) Sen­tinel-1 satel­lite – high­ly ac­cu­rate DLR transpon­ders, lo­cat­ed to the west of the Oberp­faf­fen­hofen site, are used on be­half of ESA to cal­i­brate the radar in­stru­ment aboard the Sen­tinel-1A and B satel­lites, which were launched in 2014 and 2016, re­spec­tive­ly.
DLR project team af­ter a suc­cess­ful test
Image 5/5, Credit: DLR (CC-BY 3.0).

DLR project team after a successful test

The DLR project team short­ly af­ter the first test with Radarsat-2 in Oberp­faf­fen­hofen; this test over­flight was used to check ini­tial­i­sa­tion, au­to­mat­ic align­ment, transpon­der func­tions and sig­nal cap­ture.

  • DLR supplies precision transponders to the Canadian Space Agency (CSA) for the Radarsat constellation mission
  • DLR's Microwaves and Radar Institute leads the field in the calibration of synthetic aperture radar (SAR) satellites
  • Focus: Space, Radar remote sensing, Calibration, Big Data

The calibration of radar satel­lites is a key research area at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). "In the last few years, we have earned the undisputed status of an international calibration centre for radar satellites," says Alberto Moreira, Director of the DLR Microwaves and Radar Institute. The innovative methods used for the TerraSAR-X and TanDEM-X radar satellites yielded outstanding radiometric and geometric precision. These methods were also adopted by the European Copernicus Programme for the Sen­tinel-1 mis­sion and implemented by DLR on behalf of the European Space Agency (ESA).

The supply of transponders to the Radarsat Con­stel­la­tion Mis­sion is the latest highlight in this success story. This involved the construction of two transponders with remote control capability for CSA, based on previously developed calibration targets. "Based on innovative designs we have set new benchmarks by achieving precedented precision in the development of calibration instruments in this area," explains Marco Schwerdt, Head of the Calibration Group at the Microwaves and Radar Institute. "We determine the backscatter properties of our transponders – meaning their ability to return the signal transmitted by radar satellites – to an accuracy of 0.2 decibel range and are hence on a par with highly accurate laboratory devices."

Extensive modifications were necessary to satisfy the specific requirements defined on the Canadian side and to withstand the local climatic conditions. All the electronic components, including the antennas, are located in a temperature-controlled housing in order to achieve high accuracy and reliability. The order had a value of 2.3 million euro. CSA needs the devices for its future Radarsat Con­stel­la­tion Mis­sion – a set of three SAR satellites scheduled to launch in 2019.

Precise calibration of space radar systems is necessary in order to derive geophysical information products from their data. This includes extensive measures that begin early in the development phase. Active transponders are used most frequently as calibration references due to their high backscatter cross-sections, combined with their comparatively compact structure. A radar transponder works according to the following principle – it receives the signals transmitted by the satellite, amplifies them to a highly accurate, predefined level and sends them back to the spacecraft. The transponders are shown as bright crosshairs in the radar images; the scientists use this information to calibrate the entire radar system.

DLR researchers are already working on the next generation of transponders. They will primarily focus on future long-wave missions, in particular the environmental and climate mission Tandem-L.

  • Miriam Poetter
    Cor­po­rate Com­mu­ni­ca­tions, Oberp­faf­fen­hofen, Augs­burg, Weil­heim
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 8153 28-2297
    Fax: +49 8153 28-1243
    Münchener Straße 20
    82234 Weßling
  • Dr.-Ing. Marco Schwerdt
    Head of the Cal­i­bra­tion Group
    Ger­man Aerospace Cen­ter (DLR)

    DLR Mi­crowaves and Radar In­sti­tute, Satel­lite SAR Sys­tems Oberp­faf­fen­hofen-Wessling
    Telephone: +49 8153 28-3533
    Linder Höhe
    51147 Köln
  • Dr.-Ing. Manfred Zink
    Ger­man Aerospace Cen­ter (DLR)

    DLR Mi­crowaves and Radar In­sti­tute
    Telephone: +49 8153 28-2356
    Fax: +49 8153 28-1449
    Linder Höhe
    51147 Köln
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