Misplaced Pages

#334665

60-723: As part of the payload of the MetOp series of polar-orbiting meteorological satellites , there are currently two IASI instruments in operation: on MetOp-A (launched 19 October 2006 with end of mission in November 2021), on Metop-B (launched 17 September 2012) and Metop-C launched in November 2018. IASI is a nadir-viewing instrument recording infrared emission spectra from 645 to 2760 cm at 0.25 cm resolution (0.5 cm after apodisation ). Although primarily intended to provide information in near real-time on atmospheric temperature and water vapour to support weather forecasting ,

120-780: A given value of x → {\displaystyle {\vec {x}}} , it is simply a constant scaling term. Now it is possible to solve for both the expectation value of x → {\displaystyle {\vec {x}}} , x ^ {\displaystyle {\widehat {x}}} , and for its covariance matrix by equating P ( x → | y → ) {\displaystyle P({\vec {x}}|{\vec {y}})} and P ( y → | x → ) P ( x → ) {\displaystyle P({\vec {y}}|{\vec {x}})P({\vec {x}})} . This produces

180-478: A major part of the data processing is set to be on board. As such, the transmitted data is an encoded spectrum that is band merged and roughly calibrated. Additionally, there is an offline processing chain located at the Technical Expertise Centre , also referred to as TEC. Its task is to monitor the instrument performance, to compute the level 0 and 1 initialisation parameters in relation to

240-529: A modular construction, comprising a Service Module, a Payload Module and a suite of instruments. A SPOT heritage service module provides power (via solar array and five batteries for eclipse), attitude and orbit control , thermal regulation and Tracking, Telemetry and Command (TT&C). An Envisat heritage payload module provides common command and control and power buses for the instruments along with science data acquisition and transmission. The suite of instruments are largely derived from precursors flown on

300-674: A proxy for gross primary production , can be observed using the GOME-2 instrument. The GOME-2 instrument provides a second source of ozone observations that supplement data from the SBUV/2 ozone instruments on the NOAA-18 and NOAA-19 satellites, which are part of the IJPS. One of the most important instruments carried on board Metop is the Infrared atmospheric sounding interferometer (IASI),

360-453: A radiometric calibration and an inverse Fourier transform in order to obtain the raw spectra . The central objective of the Level 0 processing is to reduce the transmission rate by calibrating the spectra in terms of radiometry and merging the spectral bands. This is divided into three processing sub-chains: Level 1 is divided into three sublevels. Its main aim is to give the best estimate of

420-593: A scan range of 48°20′ on either side of the nadir direction; the corresponding swath is then around 2×1100 km. Here, with respect to the flight direction of MetOp, the scanning executed by IASI starts on the left. Also, a nominal scan line has three targets it must cover. First, a scan of the Earth where, within each step, there are 30 (15 in each 48°20′ branch) positions at which measurements are made. In addition to that, two views dedicated to calibration - henceforth, they will be referred to as reference views . One of

480-407: A very good thermal stability for the optics of the interferometer: the temporal and spatial gradients are less than 1 °C, which is important for the radiometric calibration performance. Furthermore, other equipments are either sealed in specific enclosures, such as dissipative electronics, laser sources or thermally controlled through the thermal control section of the main structure, for example

540-468: Is also on board, linking up to buoys and other data collection devices. Metop-A, the first operational European polar-orbiting meteorological satellite, was successfully launched on 19 October 2006 from Baikonur Cosmodrome , Kazakhstan using a Soyuz-ST Fregat launch vehicle, after six attempts. At just over 4000 kg and measuring 17.6 × 6.5 × 5.2 metres when in orbit, Metop is Europe's second-largest Earth-observation satellite, after Envisat which

600-419: Is calculated as follows: This tells us, for a given element of the retrieved vector, how much of the other elements of the vector are mixed in. In the case of a retrieval of profile information, it typical indicates the altitude resolution for a given altitude. For instance if the resolution vectors for all the altitudes contain non-zero elements (to a numerical tolerance) in their four nearest neighbours, then

660-693: Is circular and has a diameter of 12 km at nadir. The shape of the IFOV at the edge of the scan line is no longer circular: across track, it measures 39 km and along track, 20 km. Lastly, the IIS field of view is a square area, the side of which has an angular width of 59.63 mrad. Within this area, there are 64×64 pixels and they measure the same area as the EFOV above. The IASI instrument produces around 1 300 000 spectra every day. It takes around 8 seconds for IASI to acquire data from one complete across track and

SECTION 10

#1732786869335

720-466: Is expected to be linear in energy, a non linearity correction is applied to the interferograms before the computation of the spectra. Next, the two reference views are used for the first step of radiometric calibration. A second step, performed on ground, is used to compensate for certain physical effects that have been ignored in the first (e.g., incidence correction for the scanning mirror, non-blackness effect etc.). A digital processing subsystem executes

780-422: Is guided by knowledge of these limitations, the resources available and the specific features of the atmosphere that wish to be investigated. In general, algorithms are based on the optimal estimation method. This essentially involves comparing the measured spectra with an a priori spectrum. Subsequently, the a priori model is contaminated with a certain amount of the item one wants to measure (e.g. SO 2 ) and

840-824: Is performed from the EPS Control Room at EUMETSAT Headquarters in Darmstadt, Germany. The control center is connected to the CDA in Svalbard which is used for S-Band ranging and doppler measurements (for orbit determination), acquisition of real-time house keeping telemetry and uplink of telecommands. The CDA at Svalbard, located at approximately 78° North, provides TT&C coverage on each orbit. Commands for routine operations are generally uplinked at each CDA contact, approximately 36 hours in advance of on-board execution. Orbit determination can also be performed using data from

900-422: Is taken to be the so-called "a-priori" distribution: x a ^ {\displaystyle {\widehat {x_{a}}}} denotes the a-priori values for x → {\displaystyle {\vec {x}}} while S x a {\displaystyle {\boldsymbol {S_{x_{a}}}}} is its covariance matrix. The nice thing about

960-541: Is the European half of the EUMETSAT / NOAA Initial Joint Polar System (IJPS). The satellites carry a payload comprising 11 scientific instruments and two which support Cospas-Sarsat Search and Rescue services. In order to provide data continuity between Metop and NOAA Polar Operational Environmental Satellites (POES), several instruments are carried on both fleets of satellites. Metop-A, launched on 19 October 2006,

1020-484: Is the matrix to be solved (the linear or linearised forward model) and S y {\displaystyle {\boldsymbol {S_{y}}}} is the covariance matrix of the vector y → {\displaystyle {\vec {y}}} . This can be similarly done for x → {\displaystyle {\vec {x}}} : Here P ( x → ) {\displaystyle P({\vec {x}})}

1080-559: Is used to provide a real-time direct readout local mission via a network of receivers on ground provided by cooperating organisations. Data from these stations is also transmitted to EUMETSAT and redistributed to provide a regional service with approximately 30 minutes latency. Due to radiation sensitivity of the HRPT hardware, the Metop-A HRPT does not operate over the polar regions or South Atlantic Anomaly . Command and Control of Metop

1140-541: Is used very commonly in the geosciences , particularly for atmospheric sounding . A matrix inverse problem looks like this: The essential concept is to transform the matrix, A , into a conditional probability and the variables, x → {\displaystyle {\vec {x}}} and y → {\displaystyle {\vec {y}}} into probability distributions by assuming Gaussian statistics and using empirically-determined covariance matrices. Typically, one expects

1200-552: The Baikonur Cosmodrome , with Metop-C being launched on 7 November 2018 from the Centre Spatial Guyanais , at Kourou spaceport , Guiana Space Centre . It was originally planned that subsequent Metop satellites will be launched at approximately five-year intervals, each having a planned operational life of 5 years - as such there would just be one operational satellite at a time. However, based on

1260-577: The European Space Agency's European Remote-Sensing Satellite ERS / Envisat satellites or are fully recurrent units originally developed for NOAA's Television Infrared Observation Satellite (TIROS) series of polar-orbiting satellites . With the exception of Search and Rescue ( SARSAT ), which is a purely local mission with its own dedicated transmitter, all data from the MetOp Instruments are formatted and multiplexed by

SECTION 20

#1732786869335

1320-597: The Iridium-Cosmos collision and Fengyun-1C anti-satellite test have significantly worsened the space debris situation in low Earth orbit (LEO). Prior to the launch of Metop-C, Metop-A and Metop-B were operated in a co-planar orbit approximately half an orbit apart. With the launch of Metop-C, the three Metop satellites initially share the same orbit separated by approximately a third of an orbit, albeit with Metop-A drifting in LTAN. However, after Summer 2020 Metop-C

1380-648: The European Space Agency MetOp Metop ( Met eorological Op erational satellite) is a series of three polar-orbiting meteorological satellites developed by the European Space Agency (ESA) and operated by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). The satellites form the space segment component of the overall EUMETSAT Polar System (EPS), which in turn

1440-425: The Exploitation of Meteorological Satellites) , the former was responsible for developing the instrument and data processing software. The latter is responsible for archiving and distributing the data to the users, as well as for operating IASI itself. Currently, Alcatel Space is the prime contractor of the project and oversees the production of the recurring models. The IASI spectral range has been chosen such that

1500-571: The GNSS Receiver for Atmospheric Sounding (GRAS) instrument. An independent back-up control center is also located at Instituto Nacional de Técnica Aeroespacial , near Madrid , Spain. The Metop and NOAA satellites both carry a common set of core instruments. In addition, Metop carries a set of new European instruments, which measure atmospheric temperature and humidity with unprecedented accuracy along with profiles of atmospheric ozone and other trace gases . Wind speed and direction over

1560-521: The Gaussian distributions is that only two parameters are needed to describe them and so the whole problem can be converted once again to matrices. Assuming that P ( x → | y → ) {\displaystyle P({\vec {x}}|{\vec {y}})} takes the following form: P ( y → ) {\displaystyle P({\vec {y}})} may be neglected since, for

1620-637: The Global Ozone Monitoring Experiment-2 (GOME-2), a scanning spectrometer on board the satellite. GOME-2, designed by DLR (the German Aerospace Centre) and developed by SELEX Galileo as the successor of ERS-2 's GOME (1995), provided coverage of most areas of planet Earth measuring the atmospheric ozone , the distribution of surface ultraviolet radiation, and the amount of nitrogen dioxide (NO 2 ). In addition, sun-induced chlorophyll fluorescence,

1680-651: The Metop satellites: Metop has been developed as a joint undertaking between the European Space Agency (ESA) and European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). Recognising the growing importance of Numerical Weather Prediction (NWP) in weather forecasting, Metop was designed with a suite of instruments to provide NWP models with high resolution global atmospheric temperature and humidity structure. Data from Metop are additionally used for atmospheric chemistry and provision of long term data sets for climate records. The Metop satellites have

1740-777: The Payload Module and either stored on a solid-state recorder for later transmission via an X-Band antenna, or directly transmitted to local users via High Rate Picture Transmission (HRPT) L-Band antenna. The main Command and Data Acquisition (CDA) head is located at Svalbard Satellite Station in Norway. The high latitude of this station allows the global data stored in the solid state recorder of each satellite to be dumped via X-Band once per orbit. Each Metop satellite produces approximately 2 GB of raw data per orbit. Additionally, in order to improve timeliness of products, one of

1800-419: The antennas and final reconfiguration of the satellite following necessary orbit control maneuvers. The satellite was handed over to EUMETSAT operations on 22 October 2006. The first image was received at 08:00 UTC on 25 October 2006 — a visible light image of Scandinavia and Eastern Europe — but there was a six-month period of verification and calibration of the satellite and its instrument payload before it

1860-562: The concentrations of various trace gases can also be retrieved from the spectra. IASI belongs to the thermal infrared (TIR) class of spaceborne instruments, which are devoted to tropospheric remote sensing . On the operational side, IASA is a replacement for the HIRS instruments, whereas on the scientific side, it continues the mission of instruments dedicated to atmospheric composition, which are also nadir viewing, Fourier Transform instruments (e.g. Atmospheric Chemistry Experiment). Thus, it blends

Infrared atmospheric sounding interferometer - Misplaced Pages Continue

1920-419: The degradation of the spectral quality. Ice accumulation on the optical surfaces determines loss of transmission. In order to reduce IASI's sensitivity to ice contamination, the emissive cavities have been added with two even holes. Moreover, it was necessary to ensure protection for the cold optics from residual contamination. To achieve this, sealing improvements have been made (bellows and joints). IASI at

1980-622: The demands imposed by both meteorology - high spatial coverage, and atmospheric chemistry - accuracy and vertical information for trace gases. Designed by the Centre national d'Études Spatiales , it now combines a good horizontal coverage and a moderate spectral resolution. Its counterpart on the Suomi NPP is the Cross-track Infrared Sounder (CrIS). Under an agreement between CNES and EUMETSAT (European Organisation for

2040-481: The end of 2022, the same fuel reserve process was enforced on Metop-B. The vast majority of fuel consumption during the operations phase is needed to compensate for inclination drift and maintain a Sun-synchronous orbit (SSO) with a mean local time of the ascending node (LTAN) of 21:30, and it is estimated that the platform can survive for at least 5 years with a drifting LTAN. These end-of-life disposal operations were initially unplanned, but are deemed necessary after

2100-505: The expected error. Alternatively, the IASI Level 1 data can be processed by least square fit algorithms. Again, the expected error must be taken into consideration. IASI's main structure comprises 6 sandwich panels that have an aluminium honeycomb core and carbon cyanate skins. Out of these, the one that supports optical sub-assemblies, electronics and mechanisms is called the main panel . The instrument's thermal architecture

2160-399: The first Metop-SG, such that a tandem mission between Metop-SGA1 and Metop-C can be performed to cross calibrate old and new instruments. After the tandem mission all Metops will be phased such that they are either half or quarter of an orbit apart. Optimal estimation In applied statistics, optimal estimation is a regularized matrix inverse method based on Bayes' theorem . It

2220-410: The following equations: Because we are using Gaussians, the expected value is equivalent to the maximum likely value, and so this is also a form of maximum likelihood estimation. Typically with optimal estimation, in addition to the vector of retrieved quantities, one extra matrix is returned along with the covariance matrix. This is sometimes called the resolution matrix or the averaging kernel and

2280-466: The geometry of the interferometer at the time of the measurement. Several of the parameters of the estimation model are computing by the TEC processing chain and serve as input for the Level 1 estimations. The estimation model is used as a basis to compute a more accurate model by calculating the corresponding spectral calibration and apodisation functions. This allows the removal of all spectral variability of

2340-725: The good performance of both the Metop-A and Metop-B satellites, EUMETSAT council agreed to extend the EPS programme until at least 2027. Metop-A was operated until 30 November 2021, and similar extensions are projected for Metop-B and Metop-C. The last Metop-A Out of Plane manoeuvre was performed in August 2016, almost all remaining fuel on board Metop-A was budgeted for end-of-life disposal operations required to put Metop-A in an orbit which will decay and cause re-entry within 25 years in accordance with ISO 24113 Space Debris Mitigation Guidelines. At

2400-455: The instrument can record data from the following ranges: As such, the spectral range of IASI is 645 – 2760 cm (15.5 - 3.62 μm). It has 8461 spectral samples that are aligned in 3 bands within the spectral range, shown in the table below. Correspondingly, the spectral resolution at which the measurements are made is 0.5 cm. Each band has a specific purpose, as shown in the following table: As an across track scanning system , IASI has

2460-686: The measurements. This level is concerned with deriving geophysical parameters from the radiance measurements: The processes here are performed synergically with the ATOVS instrument suite, AVHRR and forecast data from numerical weather prediction. Some researchers prefer to use their own retrieval algorithms, which process Level 1 data, while others use directly the IASI Level 2 data. Multiple algorithms exist to produce Level 2 data, which differ in their assumptions and formulation and will therefore have different strengths and weaknesses (which can be investigated by intercomparison studies). The choice of algorithm

Infrared atmospheric sounding interferometer - Misplaced Pages Continue

2520-473: The most accurate infrared sounding interferometer currently in orbit. IASI observes the atmosphere in the infra-red (3.7 – 15.5 μm) in 8461 channels, allowing to measure the atmosphere temperature within 1 °C and relative humidity within 10% for each slice of 1 km height. Earth surface is revisited twice a day. IASI by itself produces half of all Metop data. Metop-A and Metop-B were launched respectively on 19 October 2006 and 17 September 2012, from

2580-544: The oceans will also be measured. It is expected that these new instruments will herald a significant contribution to the ever-growing need for fast and accurate global data to improve numerical weather prediction. This in turn will lead to more-reliable weather forecasts and, in the longer-term, help with monitoring changing climates more accurately. In addition to its meteorological uses, it will provide imagery of land and ocean surfaces as well as search and rescue equipment to aid ships and aircraft in distress. A data relay system

2640-406: The onboard calibration. The former consists of 120 interferograms, each one corresponding to one pixel. Of course, as researchers are really interested in the spectra, the data gathered by IASI has to pass through several stages of processing. Furthermore, IASI has an allocated data transmission rate of 1.5 Megabits (Mb) per second. However, the data production rate is 45 Mbit/s and therefore,

2700-653: The operational satellites dumps the data from the descending part of the orbit over the McMurdo Station in Antarctica . Data are then trickle fed from the ground stations to EUMETSAT Headquarters in Darmstadt , Germany, where they are processed, stored and disseminated to various agencies and organisations with a latency of approximately 2 hours without the McMurdo ground station and 1 hour with Svalbard. HRPT

2760-496: The orbit of Metop-A and decommissioned the spacecraft in November 2021 The successor to the Metop satellites will be MetOp-SG , currently with the first MetOp SG-A satellite expected to be launched in 2025. The following instruments are flown on board the Metop satellites: The following instruments are shared on the NPOES satellites which form the U.S. contribution to IJPS: The following instruments are flown exclusively on

2820-413: The physical state of the atmosphere that was observed. The first two levels are dedicated to transforming the interferograms into spectra that are fully calibrated and independent of the state of the instrument at any given time. By contrast, the third is dedicated to the retrieval of meaningful parameters not only from IASI, but from other instruments from MetOp as well. For example, since the instrument

2880-563: The preceding point and to compute the long-term varying IASI products, as well as to monitor the Near Real Time (NTR) processing (i.e. levels 0 and 1). There are three such processing levels for the IASI data, numbered from 0 to 2. First, Level 0 data gives the raw output of the detectors, which Level 1 transforms into spectra by applying FFT and the necessary calibrations, and finally, Level 2 executes retrieval techniques so as to describe

2940-454: The primary Metop satellite has decreased in relative terms since 2011 from 24.5% to 11.15% in the FSOI metric. (The social and economic benefits of EPS-Aeolus and EPS-Sterna). Each of the three satellites were originally intended to be operated sequentially, however good performance of the Metop-A and Metop-B satellites mean there was a period of all three satellite operating. EUMETSAT lowered

3000-406: The resulting spectra are once again compared to the measured ones. The process is repeated again and again, the aim being to adjust the amount of contaminants such that simulated spectrum resembles the measured one as closely as possible. It must be noted that a variety of errors must be taken into consideration while perturbing the a priori, such as the error on the a priori, the instrumental error or

3060-416: The scan mechanisms or the blackbody. Upon entering the interferometer, the light will encounter the following instruments: So as to reduce the instrument background and thermo-elerctronic detector noise, the temperature of the cold box is maintained at 93 K by a passive cryogenic cooler. This was preferred to a cryogenic machine due to the fact that the vibration levels of the latter can potential cause

SECTION 50

#1732786869335

3120-522: The statistics of most measurements to be Gaussian . So for example for P ( y → | x → ) {\displaystyle P({\vec {y}}|{\vec {x}})} , we can write: where m and n are the numbers of elements in x → {\displaystyle {\vec {x}}} and y → {\displaystyle {\vec {y}}} respectively A {\displaystyle {\boldsymbol {A}}}

3180-403: The two is directed into deep space (cold reference), while the other is observing the internal black body (hot reference). The elementary (or effective) field of view (EFOV) is defined as the useful field of view at each scan position. Each such element consists of a 2×2 circular pixel matrix of what is called instantaneous fields of view (IFOV) . Each of the four pixels projected on the ground

3240-483: Was Europe's first polar orbiting satellite used for operational meteorology. With respect to its primary mission of providing data for Numerical Weather Prediction , studies have shown that Metop-A data was measured as having the largest impact of any individual satellite platform on reducing 24-hour forecasting errors, and accounted for about 25% of the total impact on global forecast error reduction across all data sources. A 2023 report updated this estimate stating that

3300-601: Was declared operational. Before that point, the Met Office received data and started to test and then use it as input to the operational numerical weather prediction runs. Metop-A was declared fully operational in mid-May 2007 and the full data of its 11 scientific instruments are available to its users on operational basis Metop-B was declared fully operational and pronounced to replace Metop-A as "EUMETSAT's prime operational SSO weather satellite" in April 2013. Metop-C

3360-563: Was decommissioned on 30 November 2021, after which only Metop-B and C remain phased approximately 180 degrees apart. The final Out of Plane manoeuvre was performed on Metop-B in September 2022 meaning that Metop-B is following a similar LTAN drift strategy to Metop-A, but 6 years later. Due to LTAN drift, Metop-B left the reference orbit ground track in October 2023, to ensure phase separation with Metop-C. Metops will be rephased after launch of

3420-453: Was engineered to split IASI in independent enclosures, optimising the design of every such enclosure in particular. For example, the optical components can be found in a closed volume containing only low dissipative elements, while the cube corners are exterior to this volume. Furthermore, the enclosure which contains the interferometer is almost entirely decoupled from the rest of the instrument by Multi-Layer Insulation (MLI) . This determines

3480-493: Was launched in 2002. The first signal from the satellite was received at 18:35 BST on 20 October 2006, and it was confirmed that the satellite was in its nominally correct orbit with the solar panel deployed. Control of the satellite was with the European Space Operations Centre (ESOC — part of ESA) which had the responsibility of achieving the final positioning of the satellite, deployment of all

3540-414: Was relocated to be approximately half an orbit apart from Metop-B, with Metop-A held between the other Metops in preparation for its disposal. Metop-B and Metop-C High Rate Picture Transmission (HRPT) transmits real-time data continuously. Metop-A had its orbit lowered by performing 23 apogee manoeuvres to almost empty its fuel tanks and is expected to re-enter the Earth's atmosphere within 25 years. Metop-A

3600-631: Was scheduled for launch towards the end of 2016, which was postponed until 2017 and was launched successfully on 7 November 2018. Due to the longer than expected in-orbit performance of Metop-A and Metop-B, all three Metop spacecraft were operated simultaneously until decommissioning of Metop-A, Metop-B and eventually Metop-C. Metop spacecraft will be succeeded in their operational role by the MetOp Second Generation satellites. EUMETSAT began de-orbiting Metop-A in November 2021 The first atmospheric contributions by Metop-A were made by

#334665