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INSTRUMENTS

Explore the many instruments the European Space Agency use to observe the Earth. ESA offer data from a wide range of optical, radar, atmospheric, altimetric and gravimetric instrumentation.

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  • Instrument - Radar Altimeters

    Instrument - Radar Altimeters

    RA (ERS)

    The Radar Altimeter (RA) was a Ku-band (13.8 GHz) nadir-pointing active microwave sensor, on board ERS-1 and ERS-2 missions, designed to measure echoes from ocean and ice surfaces.

  • Instrument - Imaging Radars

    Instrument - Imaging Radars

    PALSAR

    The ALOS PALSAR was a successor sensor to the synthetic aperture radar on board JERS-1.

  • Instrument - Spectrometers

    Instrument - Spectrometers

    SCIAMACHY Auxiliary Data

    In these cases, default values for the calibration parameters (Leakage current, Pixel-to-Pixel Gain and Etalon, Spectral calibration, a...

  • Instrument - Imaging Radars

    Instrument - Imaging Radars

    PALSAR Processor Releases

    Processor Releases The current ALOS PALSAR IPF integrated within the ESA On-The-Fly system is v4

  • Instrument - Scatterometers

    Instrument - Scatterometers

    SAR (ERS) Processor Releases

    Processor Releases It should be noted that for SAR, each product ordered is processed directly from the raw data, using the current vers...

  • Instrument - Interferometers

    Instrument - Interferometers

    MIPAS Quality Control Reports

    Quality Control Reports Products Availability This section provides information about the completeness of the latest MIPAS processed data sets (Level 0, Level 1b, and Level 2). Details about processed products, orbits with calibrations, instrument anomalies and missing measurements are given on a calendar basis for the full mission. Read more Products Anomalies During the generation of Level 1b and Level 2 products, processing exceptions or anomalies were discovered. This section provides brief descriptions of the problems and the lists of the affected products. The main objective of the MIPAS Monthly Reports was to give, on a regular basis, the status of the instrument performance, data acquisition, results of anomaly investigations, calibration activities and validation campaigns. The reports were created by the Instrument Data quality Evaluation and Analysis (IDEAS) team based on analysis, results and inputs received from other groups working on MIPAS. Read more Monthly Maps This section provides monthly mean maps of the main species measured by MIPAS. The following target parameters are considered: Temperature, H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, ClONO2, N2O5, CFC-12. Maps are currently available only for a limited part of the mission. Read more Daily Quality Reports The main objective of the MIPAS Daily Reports is to provide a daily monitoring of the mission; the daily reports allow a quick detection of any anomaly of the instrument performance or data processing. The monitoring and reporting was performed using the QUADAS tool, which ingests the products into long term databases and generates HTML reports. The quality monitoring was implemented for all the levels of production and includes format, content and consistency checks. Read more Daily Maps This section provides MIPAS Level 2 maps of daily mean at different isentropic levels. The following target parameters are considered: Temperature, H2O, O3, HNO3, CH4, N2O. Maps are currently available only for a limited part of the mission. Read more

  • Instrument - Imaging Spectrometers/Radiometers

    Instrument - Imaging Spectrometers/Radiometers

    Products Availability L0

    The current list of gaps in the AATSR Level 0 dataset is available here

  • Instrument - Imaging Radars

    Instrument - Imaging Radars

    ASAR Processor Releases

    03 3 July 2015 (current version used in processing) 6

  • Instrument - Imaging Radars

    Instrument - Imaging Radars

    ASAR Products Information

    Products Information The information provided in this page is applicable to the latest ASAR products. Level 0 products are derived from the raw satellite data and are the lowest level product available. Level 1 products are then processed from L0 products. Higher level products (Level 2) can then be derived from L1 products; however, this is currently only done with Wave mode. The general layout for all products includes the following records: Main Product Header (MPH) - The MPH has a fixed length and the format is identical across all Envisat products. Specific Product Header (SPH) - The SPH is defined for each product and provides additional information related to the processing, which is applicable to the whole product. Data Set (DS) - The DS contains the instrument's scientific measurements that are either measurement data sets (MDS) or annotation data sets (ADS). Further details are provided in the ASAR product specifications. All ASAR products are provided in ENVISAT format and are processed by the ESA PF-ASAR processor. For information on the latest version of PF-ASAR, see the Processor Releases page. The specifications for the ASAR data products currently made available by ESA are shown in the ASAR Product Table below. Detailed information on all ASAR products can be found in the ASAR Product Handbook. ASAR L1 product types. *Range width depends on swath used Product ID Product Name Nominal resolution (m - range x azimuth) Pixel Spacing (m) Coverage (km - range x azimuth) Equivalent No. Looks IMP_1P Image Mode Precision 30 x 30 12.5 56-100 x 100 >3 IMS_1P Image Mode Single-Look Complex 9 x 6 natural 56-100 x 100 1 IMM_1P Image Mode Medium resolution 150 x 150 75 56-100 x 100 40 APP_1P Alternating Polarisation Precision Image 30 x 30 12.5 41-106 x 100 >1.8 APS_1P Alternating Polarisation Single-Look Complex 9 x 12 natural 41-106 x 100 1 APM_1P Alternating Polarisation Medium resolution 150 x 150 75 41-106 x 100 50 WSM_1P Wide Swath Mode Medium resolution 150 x 150 75 400x 400 11.5 WSS_1P Wide Swath Mode Single-Look Complex 11.5-20 x 117 7.8x80 400x 400 1 GM1_1P Global Monitoring Mode Image 1000 x 1000 500 400x 400 7-9 WVI_1P Wave Mode Imagette and power spectrum 9 x 6 natural 5 x 5 1 WVS_1P Wave Mode Image Spectra - - 5 x 5 - WVW_2P Wave Mode Ocean Wave Spectra - - 5 x 5 - All ASAR L0, High- and Medium resolution Level 1 imagery data products are made available through the ESA (A)SAR Online Dissemination Service (OTF). L1 and L2 ASAR Wave products are accessible from the ESA Dissharm FTP server after specific product registration. The data are freely available to ESA EO Sign In registered users. High Resolution products High resolution products are processed from the Level 0 data upon request using the (A)SAR On-The-Fly (OTF) service launched in September 2016. These products are not archived but are processed when a product is selected, usually becoming available within a few minutes. The Level 1 products processed in this manner are: ASA_IMP_1P ASA_IMS_1P ASA_APP_1P ASA_APS_1P ASA_WSS_1P Although nominally only L1 products are made available, limited amounts of the following Level 0 (L0) products are available for direct download upon submission and approval of a data service request: ASA_IM__0P ASA_AP_0P (including Co-polar (APC), Cross-polar horizontal (APH) and Cross-polar vertical (APV) ASA_WS__0P Medium Resolution products The ASAR medium resolution Level 1 products have been processed from the Level 0 data during a bulk processing activity. Therefore, also these products have been archived and are available for direct download through the ESA (A)SAR Online Dissemination Service. The products available in this manner are: ASA_IMM_1P ASA_APM_1P ASA_WSM_1P ASA_GM1_1P Once registered, users can access the Level 1 OTF standard service using the ESA (A)SAR Online Dissemination Service To download the products users will need to log in using their ESA EO Sign In account. For more details on the service, please see the links for the Data Descriptions of interest and the (A)SAR Online Dissemination Service FAQ page. Wave products Wave products were processed operationally using the version of PF-ASAR available at the time of processing. Therefore, these products have been archived and are available for immediate download. The products available in this manner are: ASA_WVI_1P ASA_WVS_1P ASA_WVW_2P Once registered, users can access the Level 1 and Level 2 wave products though the ESA Dissharm FTP server (envwave-ftp-ds.eo.esa.int) using the credentials provided at registration. Information on ASAR Wave Mode data can be found in the 'Envisat ASAR Wave Mode Product Description and Reconstruction Procedure' document. The purpose of this document is to provide the user community with information to reconstruct and interpret the ocean wave spectral information within the ASAR WV products.

  • Instrument - Scatterometers

    Instrument - Scatterometers

    WS Processor Releases

    The current processor software version for the operational ground segment is ASPS v 10

  • Instrument - Imaging Radars

    Instrument - Imaging Radars

    PALSAR Quality Control Reports

    Read more ALOS PALSAR Quality Disclaimer A small percentage of ALOS PALSAR products processed by the current installed ESA IPF are affe...

  • Instrument - Radar Altimeters

    Instrument - Radar Altimeters

    RA (ERS) Overview

    RA Applications Significant Wave Height Measured by the ERS Radar Altimeter The ERS Radar Altimeter (RA) operated in two modes: ocean mode and ice mode. The RA operated by timing the two-way delay for a short duration radio frequency pulse, transmitted vertically downwards. The required level of range measurement accuracy (better than 10 cm) calls for a pulse compression technique (chirp). The instrument employed frequency modulation and spectrum analysis of the pulse shape. In ocean mode a chirped pulse of 20 micro-s duration was generated with a band width of 330 MHz. For tracking in ice mode an increased dynamic range is used, obtained by reducing the chirp bandwidth by a factor of four to 82.5 MHz, though resulting in a coarser resolution. The Radar Altimeter for ERS-1 and ERS-2 was designed to meet very demanding constraints and had the following major objectives: Precise altitude (ocean surface elevation for the study of ocean currents, the tides and the global geoid) - global measurements of the height of the ocean waves (as significant wave height) - such measurements are extremely important to marine users and scientists wishing to understand the ocean's dynamic behaviour. The Radar Altimeter provided measurements to latitude 82°, north and south, extending to regions which previously had no regular observations - this included the major wave-generation regions in the Southern oceans. Significant wave height (SWH) - measurements of the satellite's height above the local mean sea surface, with an unprecedented precision (equivalent to 1 cm in 100 km) - the applications of this dataset are numerous, for example the operational monitoring of the boundaries of major ocean currents, likely to have significant economic benefits. Ocean surface wind speed - global measurements of wind speed - these can be used to complement the SAR and Scatterometer wind field measurements and also combined with the Radar Altimeter measurements of SWH to distinguish swell from wind-driven waves. Various ice parameters (surface topography, ice types, sea/ice boundaries) - the ability to make measurements over ice with the long term monitoring of the topography of the ice sheets providing a vital warning capability for any substantial shift in the world's climate. Design ERS-2 platform and payload The Radar Altimeter antenna consisted of a reflector, waveguide feed, tripod plus supporting structure, horn feed and the waveguide. In ocean mode a chirped pulse of 20 micro-s duration was generated with a band width of 330 MHz. For tracking in ice mode an increased dynamic range is used, obtained by reducing the chirp bandwidth by a factor of four to 82.5 MHz, though resulting in a coarser resolution. The Frequency Generator units provided the transmit signal at a frequency of 450 MHz to the chirp generator. This generated a chirped output with a bandwidth of 165 MHz (ocean) and 41.25 MHz (ice), gated within a pulse of 20 micro-s. This signal was up-converted and multiplied (using C- and L-band LO signals) to 13.8 GHz, with 330 MHz (ocean) and 82.5 MHz (ice) bandwidths. The required power output level (42 dBm) was generated by the High Power Amplifier (HPA), which was realised as a Travelling Wave Tube and Electronic Power Conditioner (TWT/EPC) combination. A harmonic filter at the TWT output attenuated the harmonics of the RF signal. The transmitter signal was fed to the antenna. The returned signal was routed to the receiver via the Front End Electronics, with an insertion loss of approximately 1.6 dB. The received chirp signal was deramped by mixing it with the LO chirp at a frequency of 15.025 GHz. The deramped output (first IF) was at 1.225 GHz. The signal was then amplified to recover the conversion loss, filtered and mixed with a second LO chirp (1.3 GHz) to provide a second IF of 75 MHz. The second IF signal was filtered, using a surface acoustic wave (SAW) device with a bandwidth of 3.2 MHz and passed via a step attenuator. This provided an overall gain adjustment over a 62 dB range, implemented as two 31 dB step attentuators with a step size of 1 dB. The output was then coherently detected by a quadrature IF mixer to obtain the I- and Q-components of the received signal. The Processor and Data Handling Sub-system (PDHSS) performed tracking and the necessary processing of the radar echoes in order to maintain the echo within the radar range-window. Measurements over ocean The return pulse shape as a function of time is the convolution of three functions: the average flat surface impulse response, which is a function incorporating the antenna beam weighting and the geometric spreading of the radar pulse along the original surface the probability distribution of surface heights over the sea surface, expressed in terms of delay times the altimeter system point-target response, which is a function of pulse width Over ocean surfaces, the distribution of the heights of reflecting facets is gaussian or near-gaussian, and the echo waveform has a characteristic shape that can be described analytically, as a function of the standard deviation of the distribution which is closely related to the ocean wave height. The resulting return pulse shape is shown in the figure. In general terms the ocean mode encompassed the following echo characteristics: time delay with respect to the transmitted pulse - this provides the measure of altitude; slope of the echo leading edge, which is related to the width of the height distribution of reflecting facets, and thus to wave height parameters such as SWH; the power level of the echo signal, which depends on small scale surface roughness, and thus on surface wind-field parameters over the ocean. Real echoes are composed of the sums of signals from many point scatterers, each with individual phase and amplitude. Therefore, the individual echoes have statistical characteristics superimposed on the pulse shape. In order to reduce uncertainties in the determination of pulse characteristics, the altimeter averages pulses together to reduce this statistical effect. When in ocean tracking mode, the mean sea-level point (mid point of the leading edge) on the time axis is maintained in the centre of the range window. The time interval between the transmitted pulse and this point is effectively the classical radar measurement of range. Measurements over ice From other surfaces the waveform shape does not always conform to the simple Brown Model. The return echo from sea ice appears more specular than that from the ocean and has a peaked trace. The variability of the range measurement is of the same order as that from the ocean and this surface can therefore be tracked using the altimeter ocean tracking mode. The situation is different for continental ice, as the typical return echo has unpredictable shape and more importantly can have a larger variability in surface elevation An altimeter waveform over continental ice where the typical return echo has unpredictable shape and can have a larger variability in surface elevation. In order to maintain track of the surface, the Radar Altimeter, in ice mode, benefited from a wider observation window. The required increase in the size of the observation window was obtained by reducing the pulse bandwidth by a factor of four. This solution did not change the intermediate frequency (IF) bandwidth and was equivalent to enlarging the filter bandwidth without changing the filter bank; therefore it did not introduce major hardware changes into the system. In ice mode, tracking the echo of unpredictable shape was achieved by tracking the centre of gravity of the return pulse rather than the leading edge. This technique was used as the location of the centre of gravity is always unique, whereas there may be more than one leading edge, so avoiding any ambiguities. The main instrument parameters and technical characteristics of the Radar Altimeter Mass: <= 96 kg Antenna diameter: 1.2 m DC power: <=134.5 W Data rate: <= 15 kbit/sec Bandwidth: ocean mode: 330 MHz ice mode: 82.5 MHz Pulse repetition frequency: 1020 Hz RF transmit power: 50 W Pulse length: 20 micro-s chirp Altitude measurement: 10 cm (1s, SWH = 16 m) Significant wave height: 0.5 m or 10% (1s) whichever is smaller Backscatter coefficient: 0.7 dB (1s) Echo waveform samples: 64 x 16 bits at 20 Hz Beam width: 1.3° Sea surface elevation: better than 10 cm Spatial Resolution: Footprint is 16 km - 20 km, depending on sea state Waveband: Microwave: Ku-band: 13.8GHz Sensor Modes ERS Radar Altimeter sea level map The ERS Radar Altimeter operated in 2 modes: ocean mode and ice mode. Beam width = 1.3° foot print = 16 - 20 m (depending on sea state). RA-1 operated by timing the two-way delay for a short duration radio frequency pulse, transmitted vertically downwards. The required level of range measurement accuracy (better than 10 cm) calls for a pulse compression technique (chirp). The instrument employs frequency modulation and spectrum analysis of the pulse shape. RA-1 provided measurements leading to the determination of: Precise altitude (ocean surface elevation for the study of ocean currents, the tides and the global geoid) Significant wave height Ocean surface wind speed Various ice parameters (surface topography, ice types, sea/ice boundaries) More details about RA (ERS-2) Sensor Modes are available in an ESA Bulletin Instrument Operations Find out about RA (ERS-2) instrument operations

  • Instrument - Spectrometers

    Instrument - Spectrometers

    Products Availability L1

    04-W Number of Orbits Year Planned Available Not recoverable* Failed or Missing Current Availability (%) 2002 2176 1817 319 40 97

  • Instrument - Interferometers

    Instrument - Interferometers

    Products Availability L0

    This page provides an overview of the completeness of the MIPAS Level 0 dataset, starting from the 1st of July 2002 until the end of the ENVISAT mission (8 April 2012). The table below shows a statistics of Level 0 products availability. Click on each year to obtain a calendar view with the list of available orbits. Click on the number of available products to get the full list of products for that year. Last update on 29 March 2017 - Issue 1.3 Year Total orbits Products available Percentage of availability Products currently being retrieved Products not recoverable (*) 2002 (since 01/07) 2634 2054 98,61 % 29 551 2003 5224 4580 99,78 % 10 634 2004 5239 1205 98,61% 17 4017 2005 5225 1764 99,05% 17 3444 2006 5225 2111 98,46% 33 3081 2007 5224 3353 99,73% 9 1862 2008 5240 4855 100,00% 0 385 2009 5224 4905 100,00% 0 319 2010 5229 4861 99,88% 6 362 2011 5243 4908 99,94% 3 332 2012 (up to 08/04) 1415 1360 99,85 2 53 Total 51122 35956 99,65% (**) 391 15058 (*) due to LOS calibration, reduced duty cycle, instrument, platform or ground segment unavailability. (**)Statistics based on the products potentially retrievable (and excluding the products not recoverable)

  • Instrument - Spectrometers

    Instrument - Spectrometers

    SCIAMACHY Quality Control Reports

    Quality Control Reports Products Availability This is information about the completeness of the latest SCIAMACHY processed datasets (Level 0, Level 1b, and Level 2). Details about processed products, instrument anomalies, and missing measurements are given on a calendar basis for the full mission. Read More Product Anomalies During the generation of the SCIAMACHY consolidated Level 1b and Level 2 products, processing exceptions or anomalies were discovered. This section provides lists with the products affected. Read More Daily Quality Reports The main objective of the SCIAMACHY Daily Reports was to provide a daily monitoring of the mission and of the operational data processing chains. The daily reports allow a quick detection of any anomaly in the instrument performance or data processing. The monitoring and reporting was performed wiith the QUADAS tool which ingested the received products into long term databases and generated HTML reports. The quality monitoring for SCIAMACHY is implemented for all levels of production and includes content and consistency checks. Read More Bi-Monthly Quality Reports The main objective of the SCIAMACHY Bi-Monthly Reports was to present, on a regular basis, the status of SCIAMACHY instrument performance, data acquisition, results of anomaly investigations, calibration activities and validation campaigns. The SCIAMACHY Bi-Monthly Reports were based on analysis results obtained by the Instrument Data quality Evaluation and Analysis (IDEAS) team, combined with inputs received from the different groups working on SCIAMACHY operation, calibration, product validation and data quality (SOST-DLR, SOST-IFE, and SRON). Read More Monthly Maps World map plots of vertical column density (VCD) values of O3, NO2, H2O, SO2, BrO, averaged over a month, were generated from consolidated Level 2 products version 5. Maps are currently available only for a limited part of the mission. Read More

  • Instrument - Scatterometers

    Instrument - Scatterometers

    WS Quality Control Reports

    Quality Control Reports Products Availability The ERS Scatterometer mission has been reprocessed with the Advanced Scatterometer Processing System (ASPS) facility, providing data with improved radiometric quality and spatial resolution. ERS-2 AMI Wind Scatterometer data set has been reprocessed covering the period from 30 December 1996 to 5 July 2011 (end of mission). Read More Cyclic Reports The cyclic reports include a summary of the daily quality control made within the IDEAS (Instrument Data quality Evaluation and Analysis Service) and various sections describing the results of the investigations related to the Scatterometer. In each section, results are shown from the beginning of the mission in order to see the evolution and to outline possible "seasonal" effects. An explanation for the major events which have impacted the performance since launch is given, and comments about the events which occurred during the cycle are included. Read More ERS-2 Yaw Error Angle Monitoring - Weekly Reports The full set of results of the yaw processing is stored in an internal ESA product named HEY (Helpful ESA Yaw). The estimation of the yaw error angle is based on the Doppler shift measured on the received echo (first three plots for the Fore, Mid and Aft antenna) and aims to compute the correct acquisition geometry for the three Scatterometer antenna throughout the entire orbit. The Yaw error angle information is also used in the radar equation to derive the calibrated backscattering from the Earth surface and to select the echo samples associated to each node in the spatial filter. Read More Cyclone Archive The activities of cyclone tracking were interrupted at the end of September 2001. The data used for these cyclone tracking activities are ERS-2 Fast Delivery scatterometer data. Read More Telemetry Data This section provides information related to the acquisition of the instrument telemetry data. The data includes instrument working modes, temperatures, currents and voltages of the transmitter and calibration chain, and finally the antenna temperatures. Read More

  • Instrument - Interferometers

    Instrument - Interferometers

    Products Availability L2

    This page provides an overview of the completeness of the MIPAS Level 2 dataset processed with ORM version 8.22 and ML2PP version 7.03, starting from the 1st of July 2002 until the end of the ENVISAT mission (8 April 2012). The table below shows a statistics of Level 2 products availability. Click on each year to obtain a calendar view with the list of available orbits. Click on the total number of available products to get the full list of products. MIPAS Level 2 ML2PP version 8.22 Last update on 12 January 2021 - Issue 1.0 Year Total orbits Products available Percentage of availability L1 products available L0 products not processed to L1b L1b products not processed to L2 2002 2634 1994 99.55 2003 49 11 (since 01/07) 2003 5224 4453 98.00 4544 5 122 2004 5239 1115 96.37 1157 39 51 2005 5225 1648 98.15 1679 75 41 2006 5225 2023 98.63 2051 59 29 2007 5224 3214 97.33 3302 50 89 2008 5240 4806 99.56 4827 27 22 2009 5224 4840 99.51 4864 39 26 2010 5229 4832 99.81 4841 20 9 2011 5243 4868 99.67 4884 23 17 2012 1415 1354 100.00 1354 6 0 (up to 08/04) Total 51122 35147 98.99 35506 392 417 MIPAS Level 2 ML2PP version 7.03 Last update on 25 May 2016 - Issue 1.0 Year Total orbits Products available Percentage of availability L0 products currently being retrieved L0 products not processed to L1b L1b products not processed to L2 L0 products not recoverable (*) 2002 (since 01/07) 2634 1881 71,41 % 120 66 20 547 2003 5224 4335 82,98 % 36 135 84 634 2004 5239 1110 21,19 % 24 74 14 4017 2005 5225 1582 30,28% 35 87 78 3443 2006 5225 1894 36,25 % 33 73 145 3080 2007 5224 3181 60,89 % 23 74 85 1861 2008 5240 4734 90,34 % 19 77 25 385 2009 5224 4845 92,75 % 8 28 24 319 2010 5229 4822 92,22 % 29 11 5 362 2011 5243 4789 91,34 % 5 107 10 332 2012 (up to 08/04) 1415 1348 95,27 % 2 12 0 53 Total 51122 34521 67,53 % 334 744 490 15033 (*) due to LOS calibration, reduced duty cycle, instrument, platform or ground segment unavailability.

  • Instrument - Spectrometers

    Instrument - Spectrometers

    Product Anomalies L2

    This page reports the anomalies identified in the SCIAMACHY data processing for the consolidated Level 1b and Level 2 data sets generated with IPF 7.04-W and SGP 5.02-W. Detailed information on affected products, anomaly investigation status, and recovery actions are provided. The status of the SCIAMACHY consolidated data sets currently available at D-PAC can be accessed here. Processing anomaly: recovery on-going Processing anomaly: recovery performed Instrument operations anomaly, not recoverable a-posteriori Mission interval Anomaly Impact IPF/SGP version Affected products Reprocessed products Published 2003/2004 Level 1b consolidated products with corrupted occultation states Read more 3 products IPF 7.04-W - - 2013-11-20 Full mission Level 1b off-line products of too short duration removed Read more 4 products IPF 7.04-W See the list - 2012-09-13 2004 & 2011 Reprocessed Level 1b off-line products from improved consolidated Level 0 files Read more 18 products IPF 7.04-W See the list See the list 2012-08-06 2011 Duplicated Level 1b off-line product Read more 45 products IPF 7.04-W See the list - 2012-08-03 Jul. 2011 Duplicated Level 1b off-line product Read more 1 product IPF 7.04-W See the list - 2012-05-25 Oct. 2011 - Nov. 2011 Reprocessed Level 1b and Level 2 off-line products from improved consolidated Level 0 files. Read more 6 products IPF 7.04-W SGP 5.02-W See the list See the list Updated 2012-05-09 Oct. 2011 - Mar. 2012 Duplicated Level 2 off-line products Read more 69 products SGP 5.02-W See the list - Updated 2012-04-04 2002 - 2003 Incorrect Level 1b products Read more 27 products IPF 7.04-W See the list See the list Updated 2012-05-09 Sep. 2011 - Mar. 2012 Duplicated Level 1b off-line products Read more 74 products IPF 7.04-W See the list - Updated 2012-04-02 Nov. 2011 - Jan. 2012 Reprocessing of Level 2 consolidated products with incorrect file size and measurement coverage. Read more 114 products SGP 5.02 See the list See the list 2012-01-11 Full-mission Level 1b off-line products generated without restituted attitude file. Read more 224 products IPF 7.04-W See the list - Updated 2012-05-09 Full-mission Level 1b off-line products generated with predicted orbit state vector instead of the expected restituted information. Read more 607 products IPF 7.04-W See the list - Updated 2012-05-09

  • Instrument - Scatterometers

    Instrument - Scatterometers

    SAR (ERS)

    Processor Releases It should be noted that for SAR, each product ordered is processed directly from the raw data, using the current ver...

  • Instrument - Scatterometers

    Instrument - Scatterometers

    SAR (ERS) Interferometry

    ERS SAR Interferometry The basic idea of interferometry is that the height of a point on Earth's surface can be reconstructed from the phase difference between two signals arriving at two antenna. This is because the phase difference is directly related to the difference in path lengths traversed by the signal between the point on the Earth surface and the two antennae. If the positions of the antennae are known accurately then the path difference can be used to infer the position of the target point on Earth's surface. The basic requirements for a repeat pass interferometric system (such as the use of ERS-1 or tandem ERS-1 / ERS-2) can be stated as: stable terrain backscatter (i.e. slowly changing) similar atmospheric conditions during acquisitions stable viewing geometry preservation of inherent phase information within the SAR processor Unfortunately, in practice, the accurate determination of the terrain height over the InSAR dataset is difficult. This is due to a number of reasons which arise at different points in the generation, processing and application of interferograms and result in one or more of the criteria listed above not being met. In order to categorise these effects it is necessary to know precisely how InSAR can be used to generate height information and to what uses this information can be put. There are four stages to the reconstruction of height information from the raw images: Coregistration of the complex SAR images: as the second image is acquired from a different viewing point to the first reference image, the data in the second image must be resampled so that the second image can be projected on to the first image Interferogram formation: this is calculated by multiplying the second image by the complex conjugate of the first image. The fact that the image data retains both amplitude and phase information means that the file size is somewhat larger than the more familiar intensity images. The interferogram is a method for illustrating the variation of phase difference over the image although there is an ambiguity of ñ2Np where N is an integer. Interferogramme are conventionally visualised using a Red- Green-Blue composite image where different information is assigned to each of the channels. One typical scheme is to assign the red channel to the coherence estimate (which can be calculated using a variety of methods), the green channel to the phase difference between pixels in the two images and the blue channel to the average intensity. Phase unwrapping: The problem of adding the correct number of multiples of 2p to the interferogramme in order to extract height information is referred to as phase unwrapping. There are a number of methods for attempting this stage of the processing including: the Goldstein branch cut method the fringe detection method of Lin et al knowledge injection DEM construction At each processing stage, there are various problems that must be overcome. Some of the problems are outlined below: Noise: the major sources of noise lead to problems mainly in the coregistration of the images and the phase unwrapping. Noise values lead to a loss of coherence and a degradation of the observed fringes. Atmospheric effects: local variations in atmospheric properties lead to differences in the path lengths between the two antenna positions and the target area giving rise to spurious phase variations which are superimposed on to the phase variations generated by the target area. Environmental effects: effects such as layover lead to discontinuities in the phase variations. In addition changes in environmental conditions (eg wind direction) alter the backscattering properties of the target areas between successive acquisitions leading to loss of coherence and subsequent difficulties in the production of the interferograms. In addition to the effects outlined above which give rise to degradation effects in the images and interferograms, there are several parameters which must be optimised for useful InSAR data acquisition. These include the time between acquisitions and the interferometric baseline: Temporal decorrelation: excessive time periods between successive acquisitions of SAR scenes can result in a reduction of coherence preventing the generation of interferograms due to a temporal variation in backscattering properties of the target area. The time scales vary depending on the nature of the target (e.g. for a glacier during the summer period when excessive melting may occur, successive scenes acquired one day apart may not exhibit sufficient coherence to generate interferograms. In other cases, acquisitions several years apart may allow the generation of high quality fringes. Baseline limitations: above a critical length of baseline (approximately 1100 m for ERS-1) there is a complete loss of coherence. The degree of this coherence significantly influences the accuracy of the phase and hence the height measurement. In practice, there are limitations on length of baseline for which useful interferograms can be calculated. For mapping, the optimal baseline length is between 50 m and 300 m. Shorter baselines can yield useful information regarding glacier properties but tend not to yield useful datasets for height estimation. The upper practical limit is around 600 m. The availability of satellite borne SAR data has allowed InSAR to develop at a considerable rate. Applications of InSAR InSAR techniques can provide useful information within many application fields. Depending on various factors (eg the area under study, the time between repeat acquisitions, the time of year etc) it is possible to extract very different categories of information. Some of the applications are mutually exclusive (ie when a dataset is suitable for one application it is unsuitable for another) whereas other applications can extract different signature information from the same dataset. This can cause additional problems as the signature of one type of phenomena contained within an interferogramme can be regarded as noise contaminating the signature of a different phenomenon. Examples are: DEM generation and land cover mapping: vegetation causes a strong temporal decorrelation between acquisition dates (due to changes in environmental conditions) preventing the extraction of reliable height information from the interferogramme and the subsequent construction of a DEM. On the other hand, vegetation can be categorised by the degree of decorrelation caused and thus enable the identification of different land cover types. Glacier movement and topographic mapping: separation of effects due to glacier movement induced decorrelation and topographic effects can be difficult but is a necessary step in the extraction of glacier information from the interferogrammes. In addition, components of the interferometric signal such as anomalous signal path lengths introduced by atmospheric effects are currently treated as pure noise. This is because there are currently no applications exploiting such information. At the present time there are five major applications of InSAR. These are: DEM generation: this involves the reconstruction of terrain heights from the unwrapped phase information derived from the InSAR dataset and has numerous applications including mobile telecommunications network planning, exploration geology and urban planning. An additional application is in the improved terrain correction of SAR imagery for applications in remote areas where cartographic data are out of date or unavailable. Land use classification and forest monitoring. Forest canopy height information can be extracted in suitable terrain if the coherence is sufficiently high. Different crop types can be identified based on their effects on the spatial variation of coherence within the InSAR dataset. In general, forested areas exhibit low levels of coherence (due to changes in wind conditions between acquisitions) allowing the identification f forest cover from other land cover classes. Geophysical hazard analysis (earthquakes, volcanoes, landslides and subsidence), prediction and quantification There are three principle application areas in geophysical hazard analysis: measurement of dislocation extent at the source of an earthquake measurement of small height variations due to the filling and drainage of magma chambers under volcanoes monitoring of subsidence resulting from extraction activities such as coal mining Each of these applications require a more advanced technique known as Differential Interferometry, in which very small land surface movements can be detected. The idea is to use an existing DEM or a stable (no movement) interferogramme to remove topographic effects by subtracting the terrain generated fringes from an interferogram. The resulting fringes are due to smaller motion effects. Differential Interferometry allows the measurement of movements on the scale of millimetres. Glacier motion measurement: InSAR data are used for the measurement of glacier motions and topography changes. This is important information for assessing glacier mass transport rates and changes in glacier volume which is, in turn, essential for the validation and improvement of hydrological models. In addition, such information may have significant implications for global climate change assessment. Hydrological modelling: there are two aspects to the use of InSAR data in hydrological applications: determination of ground cover and run off paths in arid regions in order to optimise run-off interception structures measurement of ground motion associated with the filling and drainage of underground reservoirs In addition to the five applications described above, there are several application areas which are currently the focus of attention regarding future applications of InSAR. These include: coastal zone and inter-tidal zone monitoring snow melt measurement These last two applications are at a less advanced stage due to particular difficulties in extracting the signal of interest from decorrelations arising due to variations in surface moisture levels. InSAR and the ERS Tandem operations The orbit maintenance and measurement strategy was such that the ERS platforms were unique in their capability to be exploited for the generation of interferometric SAR data sets. However, the ERS orbit configuration, designed before interferometry was considered as an operational technique, was not ideally suited to the production of interferometric datasets. In particular, the repeat cycle of 35 days for the major part of the ERS lifetime means that the level of coherence between successive SAR acquisitions was, in many cases, insufficient to allow the generation of interferograms. The launch of ERS-2 however, changed the situation drastically. With the potential to simultaneously operate two platforms in tandem, the time between acquisitions was reduced to ensure an adequate coherence between successive SAR scenes while maintaining each platform in an orbit configuration that ensures a maximum possible coverage of Earth's surface. The ERS Tandem Mission objectives were primarily focussed on the collection of SAR data pairs for exploitation in interferometry together with the synergistic use of instruments on the two platforms. ERS-1/ERS-2 SAR pairs with an offset of one day were acquired covering large parts of the global land surfaces. Close and efficient cooperation among all the ERS ground-segment entities enabled the collection of this unique data set which offered a chance to scientists and operational organisations to derive medium to high resolution DEMs for a variety of applications. The Tandem objectives were met by accurately adjusting the orbital positions of the two satellites. During ERS-2 Commissioning Phase and the Tandem Operations Phase the two satellites were maintained in the same orbital plane, ERS-2 following ERS-1 30 minutes later. This means that the same swath on ground was acquired by ERS-2 one day after ERS-1. In coordination with the global network of national and international receiving stations, a background acquisition plan was set up matching within the constraints of satellite resources the availability period of the station with specific orbit maintenance procedures. For example in the Polar Campaign period, the orbit was maintained to meet baseline requirements (cross track separation of 70-170 metres) at latitudes above 60° while orbit cross over points were at equatorial latitudes. During this period maximum acquisition was scheduled over the stations of O'Higgins, McMurdo, Syowa, Alaska, Prince Albert and Kiruna. In contrast, full coverages of South America (Cuiaba) were acquired in April/May, when the orbit maintenance was focused on meeting a 50-200 metres cross track separation at the equator. Loss of SAR tandem coverage due to late availability of certain receiving stations and conflicts caused by the completion of the ERS-2 WSC commissioning activities during the Tandem Phase could be compensated for by extremely precise orbit maintenance, The high frequency of in-plane manoeuvres especially towards the end of the tandem mission ensured that nearly every acquired data pair met the stringent specifications in terms of cross-track separation. In order to further strengthen the exploitation of the ERS Tandem Mission, an Announcement of Opportunity dedicated to the scientific exploitation of the data collected resulted in some 60 projects focussing on ERS InSAR techniques and complementary use of ERS-1 and ERS-2 instruments. Tandem acquisition status After nine months of operating the ERS-1 and ERS-2 spacecraft in tandem together with the ERS-2 commissioning phase, the objectives of the ERS Tandem Mission were successfully completed. The table below shows the acquisition status. Baseline range Number of frames pairs % of total Bperp < 50 m 22181 20 50 m < Bperp < 300 m 81619 73 30 0m < Bperp < 600 m 6221 6 600 m < Bperp 1028 1 Tandem acquisition statistics The data acquired during the Tandem phase with values of Bperp between 50 m and 300 m are of particular interest for InSAR applications. These are shown in greater detail in the table below. Baseline range Number of frames pairs % of total 50m < Bperp < 130 m 45681 41 130 m < Bperp < 215 m 26637 24 215 m < Bperp < 300 m 9301 8 Tandem acquisitions with baseline values between 50 m and 300 m Images A number of observations can be made regarding the Tandem acquisition status: The majority of land areas are covered. In particular (apart from Siberia) latitudes above 60º N and S are covered by at least one acquisition. For large areas of Antarctica, only one acquisition pair is available. The overlap between neighbouring tracks however, assures three acquisitions for all areas south of 63° which includes the entire Antarctic continent. For Greenland, there are two to three acquisitions over most areas of the island. The area north of 70° has three full coverages due to partial overlap between neighbouring tracks. In addition to the pairs of SAR scenes acquired for baseline values between 50 m and 300 m, a number of tandem acquisitions have also been made for baselines less than 50 m. While a separation of less than 50 m is normally too small for mapping purposes, it can allow the separation of glacier movement effects and static topographic effects within interferogrammes generated over Arctic and Antarctic regions. Acquisitions for which the baseline is less than 50 m are illustrated both in a mercator projection and a polar projection. Again, the colour coding is explained within each image caption.