Envisat Addon for DIAS
Envisat 1 is an European (ESA) environmental remote sensing spacecraft that was launched by an Ariane 5 rocket from Kourou at 01:07 UT on 1 March 2002.
The 6.5 kW, 8.1 tonne (including 319 kg of fuel) spacecraft is reported to be the most massive and expensive of the European satellites, and carries 10 sensors to monitor global warming, ozone hole and desertification. The spacecraft has a square cross-section of about 2.5 m x 2.5 m and a length of 10 m, and carries a single solar power panel of about 4 m x 12 m. The long axis (X) is perpendicular to the orbital plane, the Y-axis is along track and the Z-axis is Earth-pointing. The Earth-looking synthetic aperture radar antenna of 10 m x 1.3 m is along the Y-axis. The spacecraft carries three 30 Gbit tape recorders and one 60 Gbit solid state recorder from which the data can be dumped over selected locations like Kiruna (Sweden) or a rate of 100 Mbits/s via three X-band and three Ka-band links.
Among the instruments, the ASAR (Advanced Synthetic Aperture Radar) provides images at 5.33 GHz of land and see surfaces at the resoluton of <30 m. It has a high data rate of about 100 Mbits/s, but at 1 Mbit/s over oceans. The swath width is >100 km. GOOS (Global Ozone Monitoring by Occultation of Stars) measures ozone and other trace elements in the altitude range of 20-100 km. Its steerable telescope points to one or other of 25 bright stars until that star is seen through the dense atmosphere. The 930 nm channel enables derivation of the vertical water vapor profile, the 760 nm (oxygen) channel provides the temperature profile, and the 250-675 nm channel provides ozone profile. In all the bands the spectral resolution is about 1.0 nm or less. The profile resolution is at 1.7 km.
The MERIS (Medium Resolution Imaging Spectrometer) is primarily an ocean sensor, covering the 390-1040 nm band. The swath width of 1,150 km is covered by five identical cameras and the images are fed to the entrance slits of five grating spectrometers, each of which directs the output to CCD arrays in 15 narrow wavelength bands. The targeted features are oceanic pigmentation, vegetation and cloud cover.
The MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) is a Fourier Transform interferometer and is intended to monitor about 20 trace gases, including the CFC and NOx groups by looking at their emission lines in the 4.15-14.6 micron wavelength band from the dense layers at the horizon. The CCD detectors are held at 70 K. Data acquisition is at 530 kb/s.
The RA-2 (Radar Altimeter 2) is a 160 W, dual-frequency (13.57 GHz in Ku-band, and 3.2 GHz in S-band) instrument that determines land and ocean surface levels at an accuracy of 4 cm. Analysis of the reflected pulse shape provides the characteristics of the surface also.
The MWR (MicroWave Radiometer) is primarily intended to monitor the atmospheric humidity so as to correct the RA-2 data for humidity-caused delay. It is a Dicke type radiometer operating on 23.8 and 36.5 GHz, the beams being separated by 70 km along the ground track on either side of the nadir.
The LRR (Laser Retro-Reflector) reflects back to ground-stations the visible laser pulses, providing additional range information.
The AATSR (Advanced Along Track Scanning Radiometer) primarily seeks to extend the ERS 1 & 2 databases for sea surface temperature (SST), at an accuracy of 0.5 K. It captures surface radiation at seven wavelength bands (1.6, 3.7, 10.85, 12; 0.555, 0.67, 0.865 microns). The infrared bands provide the temperature of land and sea, and the visible bands enable vegetation monitoring. The temperature accuracy is adequate to spot nascent El Nino pockets of size 1 km or more.
The DORIS (Doppler Orbitography and Radio-positioning, Integrated by Satellite) is intended to obtain precise orbit determination by receiving dopplar-shifted microwave transmissions at 2.036 GHz and 401.25 MHz) from one or other of the several ground stations (each with three transmitting antennas either side of the ground track), through its pair of omnidirectional receiving antennas. The spacecraft’s position can be determined with 1 m accuracy and its velocity at 2.5 mm/s accuracy.
The GOMOS (Global Ozone Monitoring by Occultation of Stars) is a UV/Visible/Near-infrared limb viewing grating spectrometer, operating in a star occultation mode. GOMOS relies on the self-calibrating occultation method (which minimizes the impact of instrument degradation). GOMOS introduces a new measurement principle: using stars rather than the sun or the moon as light sources (occultation measurement method), it achieves permanent, homogeneous global coverage through the measurement of 25 to 40 stars per orbit. The optical configuration, based on two grating spectrometers (range: 250 – 950 nm), permits the measurement of stratospheric profiles of O3, H2O, NO2, NO3, aerosols and temperatures with a 1.7 km vertical resolution.
Finally, the tenth instrument, SCIAMACHY (SCanning Image Absorption spectroMeter for Atmospheric CartograpHY) is intended to analyse the emitted and scattered radiation from the stratosphere and troposhere in the extensive band of 240-2400 nm through eight wavelength channels. Polarization is also measured in seven of the channels. Many trace gases, dust storms, arctic haze, aerosols, etc, contribute to the radiation. The instrument looks down at the nadir and at the horizon. The former provides total columnar content and the later enables vertical profile derivation. A scanning mirror enables azimuthal scan of swath 1000 km segmented into 16 km x 32 km sections.
DIAS supports the following list of product-types:
- ASAR Level-0: IM ; WS