1,721,078 research outputs found
Chapter 2: ENVISAT - SCIAMACHY's Host
No full textENVISAT is Europe’s ambitious Earth Observation enterprise to study the many facets of the Earth system. It carries 10 remote sensing instruments with SCIAMACHY, MIPAS and GOMOS forming the atmospheric chemistry mission. SCIAMACHY, although provided by national space agencies to ESA, is an integral part of the payload. Orbit and attitude of ENVISAT determine the framework of SCIAMACHY’s observing capabilities. As a polar, sun-synchronous satellite, ENVISAT provides a stable platform for orbiting the Earth every 100 min. All instruments share the available on-board resources, particularly on-board data handling capabilities. The ENVISAT ground segment consists of the Flight Operation Segment for platform and instrument control and of the Payload Data Segment for measurement data acquisition, processing, archiving and dissemination. The SCIAMACHY data processing occurs at the LRAC and the D-PAC, depending on whether the data is of type level 0, 1b or 2. Access to SCIAMACHY data follows the general ENVISAT data policy with the exception that the instrument providing agencies receive a separate copy of such data
Chapter 4: Instrument Operations
No full textSCIAMACHY operations have to be highly autonomous. All instrument activities are stored on-board and activated by time-tagged commands. They execute measurements in all required viewing geometries including the unique limb/nadir matching. Observations of the Sun in occultation over the northern hemisphere and the Moon in occultation over the southern hemisphere occur at regular intervals, ranging from each orbit to each month. They are complemented by sub-solar observations. The lunar measurements need particularly accurate preparation due to the orbital motions of the Moon and ENVISAT around Earth. Both Sun and Moon occultations have to take refraction into account for the period when both targets are viewed through the lower atmosphere. Timing of SCIAMACHY measurement operations is entirely Sun or Moon related. The specified mission scenarios combine nadir, limb and eclipse measurements between Sun or Moon related events along the orbit. The smallest functional sequences are states, controlled via various parameter tables. When combining individual states, timelines are generated. Sets of states and timelines are stored on-board. Each timeline is activated by a single macrocommand. Both states and timelines can be modified from ground. Since SCIAMACHY has been provided by national agencies instrument operations is a shared enterprise between DLR/NIVR and ESA
Chapter 3: The Instrument
No full textThe objective of the SCIAMACHY mission requires the instrument to be capable of determining concentrations of a large number of trace gas species over the full vertical extent of the atmosphere from the troposphere up to the mesosphere. In addition, aerosol properties as well as pressure and temperature shall be derived. Therefore SCIAMACHY was designed as a passive imaging spectrometer, comprising a scan mirror system, a telescope and a spectrometer, controlled by thermal and electronic subsystems. Scan mirrors, telescopes and spectrometer together form the optical assembly. The scan mechanisms permit steering the line-of-sight according to the required viewing geometries. Solar radiance and irradiance are dispersed by the spectrometer into 8 channels from the UV to the SWIR range. With signals gained from the calibration unit and the Polarisation Measurement Device, the spectral and radiometric calibration of the science channels can be maintained over the mission lifetime. Thermal stability is ensured via active and passive thermal control systems including the Radiant Cooler assembly. Those units which control the entire instrument and interface electrically with the ENVISAT platform are hosted by the Electronic Assembly. SCIAMACHY was developed in a combined effort of German, Dutch and Belgian space agencies, industry and scientists and ready for the ENVISAT launch in March 2002
Chapter 6: SCIAMACHY In-orbit Operations and Performance
No full textSince the launch in early 2002 SCIAMACHY has successfully operated in low-Earth orbit for more than 8 years. For the first several months a challenging Commissioning Phase programme was executed. It successively brought SCIAMACHY into full operation mode and verified the instrument’s functional capabilities. In early August 2002 quasi-routine measurements executing nominal mission scenarios could start. In January 2003 the routine operations phase commenced. Since then SCIAMACHY is kept under strict configuration control. Because of the harsh space environment the instrument is subject to degradation, both optically and thermally. The optical performance is described by the throughput which is a measure for how optical components in a light path age with time. It also includes characterisation of optical imperfections such as scan angle dependence, channel 7 light leak and spatial stray light. Illustrating the thermal performance includes decontaminations, used to tackle the ice layers in channels 7 and 8 and configuration of the thermal control systems to respond to degradation. Finally the improvement of the line-of-sight performance by determination of mispointing angles achieved the best possible pointing knowledge. This was especially needed for the retrieval of accurate limb tangent heights. The current excellent status of SCIAMACHY is a prerequisite for successfully accomplishing the intended ENVISAT mission extension until 2013
SCIAMACHY, Monitoring the Changing Earth's Atmosphere
No full textThe German-Dutch atmospheric science instrument SCIAMACHY on the European Earth observation mission ENVISAT provides new insights into the Earth's atmosphere. The book describes the SCIAMACHY mission in detail. It starts with the requirements for doing atmospheric science from space, followed by outlining the SCIAMACHY host, i.e. ENVISAT. Several chapters deal with SCIAMACHY instrument aspects: design, operations and calibration & monitoring. The system related part of the book finishes with a description of SCIAMACHY's first years in orbit. The second part of the book is devoted to the area of science data, including retrieval algorithms, data processing and product validation. SCIAMACHY's view of the Earth's atmosphere, a tour through the atmosphere from bottom to top presenting many exciting SCIAMACHY results, finally concludes the publication
Chapter 10: SCIAMACHY's View of the Changing Earth's Atmosphere
No full textSince August 2002 SCIAMACHY delivers a wealth of high-quality data permitting to study the status of the Earth’s atmosphere. Enhanced concentrations of greenhouse gases are identified as the major source of global warming and their atmospheric concentrations are increasing. SCIAMACHY monitors the most prominent species such as CO2, CH4 and water vapour, the latter including isotope variants. Further anthropogenic impacts on the troposphere occur by emission of reactive trace gases contributing to pollution and affecting air quality. With SCIAMACHY their global, regional and even local signatures can be detected. Long-term analyses document how the emissions of NO2, SO2, HCHO, CHOCHO and CO evolve with time. In addition, the halogen cycle of polar BrO and IO, both of natural origin, is studied. The stratosphere is the layer where public interest in the Earth’s atmosphere has begun to grow with the detection of the ozone hole in the mid-1980’s. Until the mid-1990s a steady decrease has been observed in the ozone abundance. The most striking feature is the massive loss of stratospheric ozone over Antarctica during each southern spring. In order to detect possible signs of recovery, SCIAMACHY contributes to the continuous monitoring of the ozone layer, the ozone hole, Polar Stratospheric Clouds (PSC) and species impacting the ozone chemistry such as NO2, OClO and BrO. A much more poorly explored region is the mesosphere and lower thermosphere, which forms the transition between interplanetary space and the terrestrial atmosphere. This region is dominated by extraterrestrial impacts as well as couplings to the lower atmosphere. With SCIAMACHY’s limb viewing capabilities Noctilucent Clouds (NLC) are studied providing insight into generation and depletion mechanisms. At times of strong solar activity, SCIAMACHY measurements reveal how the chemistry of the upper atmosphere is disturbed. By analysis of emission lines in SCIAMACHY spectra the composition of the thermosphere above 100 km can be studied. SCIAMACHY is the first instrument to globally observe the metal layers in the upper mesosphere / lower thermosphere (MLT) region. When applying appropriate retrieval techniques it is meanwhile possible to derive vegetation information over land and phytoplankton characteristics in the oceans from SCIAMACHY data. Finally SCIAMACHY even has proven useful in planetary science by measuring spectra of our solar system neighbour Venu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Chapter 5: Calibration and Monitoring
No full textSpaceborne spectral measurements over long time periods require calibration and monitoring of the instrument as a crucial prerequisite for successful retrieval of atmospheric parameters. Calibration applies a sequence of steps to the measurement data while monitoring assesses the optical performance thus permitting degradation corrections. The parameters characterising the instrument were obtained in a sequence of on-ground calibration runs under different environmental conditions. They are stored as Key Data and serve as input when deriving calibrated spectra. Relevant calibration steps include the memory effect and non-linearity, wavelength calibration and both spectral and spatial stray light corrections. Since SCIAMACHY is sensitive to the polarisation state of the incoming light, po-larisation needs to be thoroughly taken into account. The final step performs the radiometric calibra-tion. Once in orbit, the optical performance monitoring establishes information concerning the channel and wavelength dependent degradation. From the combination of the results for the different light paths it is even possible to learn how individual optical components degrade
Chapter 8: Processing and Products
No full textSCIAMACHY data processing generates products on various levels as required by the user community. These products are either produced in the ENVISAT Payload Data Segment as operational products or by science institutes as scientific products or value-added products. Operational processing occurs in two steps – level 0-1b and level 1b-2. In both steps different timescales may apply – near-realtime, fast delivery or offline. Level 0-1b processing generates geolocated and calibrated radiances from the raw atmospheric measurements, as well as from measurements for calibration and instrument monitoring. The algorithms convert measured signals into calibrated radiances. Therefore a sequence of calibration steps has to be applied starting with correcting the memory effect and non-linearity and ending with applying the radiometric instrument response. Particular attention has to be given to the correction of polarisation and degradation. The goal of level 1b-2 processing is to provide geophysical parameters such as column densities and profiles from trace gas species as well as cloud and aerosol parameters. Nadir measurements permit retrieving total column densities or cloud and aerosol parameters. From limb observations height resolved profiles of atmospheric parameters can be inferred. Together with the scientific and value-added products the SCIAMACHY data can serve a wide range of applications
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