Product User Manual for the ARS aerosol products
Contents
1. REFERENCE O3MSAF KNMI PUM 002 1 50 amp EUMETSAT O3MSAF sue 2015 05 20 DATE 4 32 TABLE OF CONTENTS T INTRODUCTION sivisiscs cecicscesezicaracpsxntsmancaronunssuceetincantsxaeubtursunntssninussvscueneescanuinennennveate 6 We PSO Ca eee 6 We CO EE E EEEE 6 LES KE ss I A AN E EE E cence teutda lenin stadia E 6 13A PORONY INS seede E EE EE 6 1 4 Reference documentS rrrrnrrnnnnnnrvrvvrnnnnnnnrrennnnnnnnnnvernnnnnnnnnerrnnnnnannrsseennnnnnnnsseeennnnnsnee 7 2 INTRODUCTION TO EUMETSAT SATELLITE APPLICATION FACILITY ON OZONE AND ATMOSPHERIC CHEMISTRY MONITORING O3MSAF 8 2 PMS 8 ER Go EEE EEE EE EEE EE 8 2 FA EE 8 2 4 Product timeliness and dissemination uusssesenssnmumingssbninbnsnbeibeelabsdsee 9 2 S MME loM e a ea a EE 9 Si METOP AND GOME 2 Linsgensenmnineieinjememnvm Gino anrs K aSr Kesas aniio in 10 J ME Ne EE E E 10 392 GOME 2 ei errre nisnin S E EEE ER EEE RE A EEEREN EEE catia ES EEEE 10 4 ALGORITHM BACKGROUND ssssnssssssunnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn nnmnnn nnmnnn nnn nanna 12 4 1 Absorbing Aerosol Index mvrrvvrvvvrvvvrvrvrrrrrrrnrrnnnnnnnnenneronrnnrnnnnennnnnnnnnernnnrrrrnrrnnrnnnnnn 12 4 2 Interpretation cece cee ceceeeeeeee eee arr nnnnnnannnnnnnnnnnnnenntennennnnnnnnnennsennnennrnnnnnnnnnnnn 13 4 3 Level 1 Input sissies rises EE EE nettet nteneee esenee 14 A AP Level 2 Output RE rnt rrn ttn rtttntttt tt tt rsr trs rte nnn ncnbbendesedncutedndeienestets 14 4 5 Delivery time t2. 1 land 4 Cloud fraction gt 0 3 8 Cloud pressure lt 850 hPa and Cf gt 0 1 32 sun glint angle lt 18 degrees 64 sun glint angle lt 11 degrees Users are advised to use pixels with flag values exactly 0 1 4 8 33 63 but not 32 or values larger or equal than 64 5 5 4 ScatteringAngle In the north and south eastern edges of the swath there are increased values of the AAI due to geometric effects The light from the sun is scattered in a forward direction to the satellite and the algorithm does not handle this at the moment Users are advised to use pixels with scattering angles larger then 90 degrees REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue er DATE 30 32 6 PRODUCT QUALITY AND CHARACTERISTICS The product quality is determined mainly by the quality of the input parameters reflectances ozone column and surface height The ozone column and surface height are both known with a relatively high accuracy The impact of errors in the radiometric calibration can be strong though The most important example of this is the impact of instrument degradation on the AAI Instrument degradation has a strong impact on the AAI The GOME 2 AAI from MetOp A is currently suffering from scan angle dependent instrument degradation As a result there is an east west bias which amounts to 3 index points for data measured at the end of 2012 Apart from the east west bias there is an overall offset A correc
3. PMD_CloudFraction Cloud fraction from AVHRR copied directly from Lib for PMD band AAI retrievals and averaged on B1b resolution in case of MSC based retrievals PMD_SceneHomo Scene homogeneity from AVHRR copied directly geneity from L1b for PMD band AAI retrievals and averaged on B1b resolution in case of MSC based retrievals REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue DATE 27 32 5 2 Data Types The data types to be used in the HDF5 files are given in the table below Table 7 Data types for the HDF5 files String Fortran HST FORTRAN S1 C HST C S1 5 3 File name convention File names of product are following the names of the input files For GOME2 these are foreseen as having the following layout for the HDF5 format files S O3M GOME ARS 02 AAA SSSS EEEE W Z PPPP hdf5 Where AAA is the flight model number On MetOp A this number is M02 The SSSS is a placeholder for the SensingStartTime YYYYMMDDhhmmssZ the EEEE is the placeholder for the SensingEndTime also YYYYMMDDhhmmssZ the PPPP is the processing time also in the same format as SSSS and EEEE The W indicates the Processing Mode and Z indicates the Disposition Mode of the file 5 4 File size estimate 5 4 1 Estimated size of ARS output file The size of the output file can vary The size is affected by different string lengths the maximum number of profiles per set the actual number of AAI retrievals the addition of option
4. DegradedRecordP ercentag Percentage of e degraded and incomplete MDRs detected by L2 software w r t total number of read Earthshine MDRs REFERENCE O3MSAF KNMI PUM 002 i 1 50 EUMETSAT O3MSAF sue DATE 21 32 MissingDataPercentage int Percentage of 0 100 Earthshine MDR records skipped by L2 software due to time breaks or other data requirements w r t total number of read Earthshine MDRs GranuleType string Type description DP Data Product of the item DispositionMode string 1 Disposition mode O perational applied for generation of the product ReferenceTime string A reference time Date in CCSDS format mainly used for the product file names Time when the product is generated TBC AscNodeCrossingTime string Ascending Node Date in CCSDS format Crossing Date and Time AscNodeLongitude Ascending Node String Longitude ProductID String Product identifier O3M XXX x where XXX as per the are digits O3MSAF Product Requirement Document String Digital Object e g for the reprocessed Identifier issued ARS product by EUMETSAT 19 15770 EUM SAF O3M 0005 for data set products REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue EF S 5 1 2 Product Specific Metadata Group The metadata definition specific for the ARS products given in the following table The parameters are stored as attributes of the Product Specific Metadata group Table 3 Product Sp
5. GOME 2 Absorbing Aerosol Index are provided by KNMI in the framework of the EUMETSAT Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring O3M SAF
6. REFERENCE O3MSAF KNMI PUM 002 EUMETSAT 2 O3MSAF se DATE 4 32 The EUMETSAT Network of Satellite Application Facilities Ozone and Atmospheric Chemistry Monitoring PRODUCT USER MANUAL Near real time and offline Aerosol products Prepared by O N E Tuinder L G Tilstra Royal Netherlands Meteorological Institute REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue a DATE 2 32 DOCUMENT STATUS SHEET Issue Date Modified Items Reason for Change 2007 05 14 First draft version 2007 06 06 Revised after ORR A2 comments 2007 10 03 Revised after ORR A2 review 2007 10 30 Revised after ORR A2 CloseOut 2008 05 23 Product format update AscNodeCrossingLon is now a string Azimuth angles added Disposition mode updated Updates indicated in New Product Format Version 3 4 2008 09 30 Revisions for ORR B 2009 04 15 Granularity explicitly mentioned the pixel size as 40x80 km 2009 09 01 SoftwareVersion 1 20 OPF v3 6 IndexInScan represents index of the ground pixel in the scan movement not index in the MDR First spectral pixel in a Lib file usually a backscan is skipped due to incomplete information on UTC date time PCloudAdjustedToPSurface flag added to the QualityInputFlags record Update indicated in B ERWelow 2010 04 29 Software v1 23 output format v8 7 Added information on the UNS Sunglint flag and scattering angle Updated some logos Added to Geolocation group ScatteringAngl
7. al data sets to the file and possibly the compression factor in the HDF5 output file On average each PDU sized data product of ARS data is about 113Kb REFERENCE O3MSAF KNMI PUM 002 amp EUMETSAT amp OIMSAF sse DATE 28 32 5 5 Using the data 5 5 1 AAI An example of the Absorbing Aerosol Index is given in Figure 4 In this figure a large Saharan desert dust plume is transported over the Atlantic Ocean from Africa to South America 2007 06 23 AAI Me Fr F Figure 4 Absorbing Aerosol Index AAI from GOME 2 for June 23 2007 5 5 2 Quality flags Quality flags are very important as indicators for the correctness of both the input and the retrieved AAI There are two quality flag groups Qualitylnput and QualityProcessing In the input flags the types of failures are set missing data geometry wise or spectral wise or out of range invalid values In the input quality flags there is a flag for sun glint The sun glint causes a spurious AAI signal This sun glint flag in the Qualitylnput comes directly from the Level 1b and is on a scan level basis i e valid for the whole scan instead for the subpixel REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue DATE 29 32 5 5 3 SunGlintFlag There is a data record in the Data Group called SunGlintFlag This indicates on a ground pixel basis whether there is a risk of sun glint Flag is the sum of the following subflags O no sun glint
8. any aspects of the aerosol scene In the paper by de Graaf et al RD2 a sensitivity study was performed In this sensitivity study it was shown that there are at least two possibilities to create a positive residue Firstly an absorbing aerosol layer can absorb Rayleigh scattered radiation from below the layer Because the Rayleigh optical thickness is strongly wavelength dependent this creates a difference in the reflectance at two UV wavelengths relative to that of a Rayleigh atmosphere even with gray absorbers i e wavelength independent absorbing particles When the absorbing ability of the layer increases more radiation is absorbed and the deviation increases increasing the residue The same is true when the amount of atmosphere under the absorbing layer increases Secondly the aerosol absorption itself can be wavelength dependent creating a spectral difference in the TOA reflected radiation This will also create a positive residue if the absorption at the shorter wavelength is stronger even when the aerosol layer is close to the surface When the spectral absorption difference increases the residue will increase meaning that different aerosol types produce different residues under the same circumstances For an atmosphere which is dominated by scattering either by particles molecules the surface or clouds the reflectance will not deviate much from the reflectance of a Rayleigh atmosphere with an adjusted surface albedo yieldi
9. ate in the Total Ozone Mapping Spectrometer TOMS ozone retrieval algorithm As TOMS instruments have flown on various platforms from 1978 to 2006 providing nearly daily global coverage the TOMS AAI record is the longest aerosol record available and it is used extensively to investigate aerosol impact on climate and study heavy dust biomass burning and volcanic eruption events Traditionally aerosol optical thickness measurements are being made using space borne sensors operating in the visible and infrared IR where multiple scattering in the atmosphere is less important than in the ultraviolet UV and inversion calculations are relatively simple In the visible and near IR the large surface albedos of many land types make retrieval of aerosols difficult over these regions With the ongoing development of numerical radiative transfer codes and increasing computational speeds accounting for multiple scattering is no longer a problem allowing for new techniques of aerosol measurements in the UV Because the surface albedos of both land and ocean are small in the UV this wavelength range should be suitable for aerosol detection over land The AAI is derived directly from another quantity the residue which is defined in the following way Herman 1997 meas Ray r 100 gl R iog Ri 1 Rio Rio In this equation R denotes the Earth s reflectance at wavelength 2 The superscript R refers to TOA reflectances which are m
10. e 4 5 Delivery time to users user access The Aerosol Absorbing Index is classified as an NRT product and can be obtained via EUMETCast or the EUMETSAT O3MSAF archive Please see the O3MSAF website at http o3msaf fmi fi or contact the O3MSAF helpdesk at o3msaf fmi fi for more information The delivery time of the offline ARS product to the EUMETSAT O3MSAF archive will be within two weeks maximum but usually within a day or two 4 6 Geographical coverage and Granularity of the level 2 product The geographical coverage of the aerosol product is practically all of the sun lit side of the earth The swaths of the GOME 2 instrument do not cover the earth completely every day at the equator but at latitudes higher than 45 degrees there is a possibility that the same surface area is viewed more than once a day Because the algorithm uses information from the wavelength region between 340 and 380 nm the granularity of the default AAI output product is the same REFERENCE O3MSAF KNMI PUM 002 i 1 50 EUMETSAT amp OIMSAF sv EE 15 32 as the Band 2b measurements This means that with nominal conditions the pixel size is 40x80km in flight direction x cross track direction REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sse DATE 16 32 5 THE ARS AAI PRODUCT 5 1 Structure of the ARS Product File The format of the offline Level 2 ARS profile product file is HDF5 The data in the HDF5 file is organized in four grou
11. e Added to DataGroup SunGlintFlag Product updates indicated in light blue 1 01 2010 05 12 Replaced scan with ground pixel in SunGlintFlag section 1 02 2010 05 25 Added intro O3MSAF added text about ftp access Software version 1 28 OPF version 4 0 2013 06 16 amp Changes based on ORR RIDs Editorial 4 1 Output format changes 2013 05 28 Added optional UncorrectedResidue and CorrectionFactor fields to store residues not corrected for instrument degradation and the degradation correction factor Added ScanDirection and ScannerAngle Valid for Ea 1 3a b 2013 06 28 Quality Flags ail 2 amp 4 2013 09 02 Adaptation of the recommendation for Sun Glint Flag use Also use value 1 land 43 1 1 1 41 2014 04 23 Section 4 5 User Access NRT data va EUMETCast 1 42 2014 04 24 Section on Sunglint flags updated Description of the scattering angle updated 2014 11 12 Added acknowledgement instructions to Further Instructions section 1 REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue a DATE 3 32 1 44 2015 02 09 Relates to Software Version 1 32 Algorithm version 0 07 OPF version 4 01 Added cloud information from Lib on PMD resolution to output product 1 50 2015 05 20 Addition of DOI and ProductID in MetaData group Previously optional parameters CorrectionFactor and UncorrectedResidue in Datagroup now become permanent when the degradation correction is used
12. e a DATE 8 32 2 INTRODUCTION TO EUMETSAT SATELLITE APPLICATION FACILITY ON OZONE AND ATMOSPHERIC CHEMISTRY MONITORING O3MSAF 2 1 Background The need for atmospheric chemistry monitoring was first realized when severe loss of stratospheric ozone was detected over the Polar Regions At the same time increased levels of ultraviolet radiation were observed Ultraviolet radiation is known to be dangerous to humans and animals causing e g skin cancer cataract immune suppression and having harmful effects on agriculture forests and oceanic food chain In addition the global warming besides affecting the atmospheric chemistry also enhances the ozone depletion by cooling the stratosphere Combined these phenomena have immense effects on the whole planet Therefore monitoring the chemical composition of the atmosphere is a very important duty for EUMETSAT and the world wide scientific community 2 2 Objectives The main objectives of the O3MSAF are process archive validate and disseminate atmospheric composition products 03 NO2 SO2 OCIO HCHO BrO H20 aerosols and surface ultraviolet radiation utilising the satellites of EUMETSAT The majority of the O3MSAF products are based on data from the GOME 2 spectrometer onboard MetOp A satellite Another important task of the O3MSAF is the research and development in radiative transfer modelling and inversion methods for obtaining long term high quality atmospheric compositio
13. easured by GOME 2 while the superscript R refers to modelled TOA reflectances These modelled reflectances are calculated for a cloud free and aerosol free atmosphere in which only Rayleigh scattering absorption by molecules Lambertian surface reflection as well as surface absorption can take place As a result the residue is a residual term caused by the presence of cloud and REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF issu DATE 13 32 aerosols in the real scene as opposed to the modeled scene More details about the calculation of the residue can be found in the ATBD RD1 The presence of clouds tends to make the residue negative Scattering aerosols will generally do the same Absorbing aerosols on the other hand increase the residue and will lead to a positive residue For that reason the AAI is defined as the positive part of the residue The two wavelengths and that constitute the AAI wavelength pair are set to 340 and 380 nm respectively The name AAI is traditionally used for indicating absorbing aerosols for which the residue has positive values In the GOME 2 ARS product we will use the AAI as being synonymous to the residue so the full range of residue values positive as well as negative will be reported in the AAI product 4 2 Interpretation The direct interpretation of the AAI in terms of aerosol properties is difficult The residue AAV SCI is a unitless quantity that depends on m
14. ecific Metadata group contents Level 1 Usage Section Attribute name Data Description Type Wavelengths Float array Wavelengths used for calculating the AAI rank 1 FullWidthTriangle Float FullWithHalfMaximum of the reflectance averaging function around the Wavelengths above 5 1 3 Table Attibutes Attributes attached to all datasets in the Geolocation group and Data group are shown in the table below Table 4 Attributes for the geolocation and data group datasets Attribute name Data Description Type Description of the dataset e g Solar noon UV index Unit of the values in the array e g DU second FillValue same as Value in the array in case actual data value is the dataset missing ValidRangeMin same as Minimum allowed value for the data in the array the dataset ValidRangeMax same as Maximum allowed value for the data in the array the dataset 5 1 4 Geolocation Group The datasets in the Geolocation group are given in the following table The data type and value of the Unit attribute are given for each dataset REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue DATE 23 32 Table 5 Geolocation group contents Dataset name Data Description type i UTC time in CCSDS format LongitudeCenter LatitudeCenter LongitudeCorner LatitudeCorner SolarZenithAngle SolarAzimuthAngle LineOfSightZenithAngle LineOfSightAzimuthAngle RelAzimuthAngle SubSatellitePointLong
15. ed to generate the L1B or L2 EPS parent product upon which the product is based the that the Version of algorithm produced product of the parent products upon which the product is based Name Abbreviated name for the product type or rather product category number product Version of the format Latitude of the sub satellite point at start of acquisition For EPS products either the first measurement or first complete scan start point 1 50 2015 05 20 19 32 R eprocessing V alidation Date in CCSDS format O3MOOP O3MNOP O3MARS 90 to 90 REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue DATE 20 32 tbd at start of dataset SubSatellitePointStartLon Longitude of the 180 to 180 sub satellite point at start of acquisition SubSatellitePointEndLat float Latitude of the 90 to 90 sub satellite point at end of acquisition SubSatelliteP ointEndLon float Longitude of the 180 to 180 sub satellite point at end of acquisition OverallQualityFlag string Overall quality OK NOK flag for the L2 product Quality Information string Several string miscellaneous quality indicators for the L2 product DegradedRecordCount Number of degraded and incomplete Earthshine MDRs detected by L2 software Number of Earthshine MDR records skipped by L2 software due to time breaks or other data requirement failures MissingDataCount
16. ements that are located in the inner GOME 1 part of the GOME 2 swath the offset was reduced to 0 2 index points 4 For GOME 2 on MetOp B we found the MSC AAI to agree nicely with the MSC AAI from the MetOp A platform Only a small offset of 0 3 index points seems to be present REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue DATE 31 32 5 The PMD AAI from MetOp A and MetOp B show similar behaviour as the MSC AAI products The statistical analyses show that the PMD AAI from MetOp A is very close to the MSC AAI from MetOp A A small offset of 0 3 index points is found The PMD AAI from MetOp B compares reasonably with the MSC AAI from MetOp B An explanation for the differences between the MSC and PMD product is the known different radiometric calibration between MSC reflectances and PMD reflectances 6 The GOME 2 AAI products have like any other AAI product a number of characteristic properties that need to be kept in mind First of all sun glint leads to anomalously high values for the AAI Measurements affected by sun glint should therefore not be used A sun glint flag is present in the product for filtering out sun glint situations Secondly solar eclipse events lead to very high and unphysical values for the AAI These data should not be used Thirdly the GOME 2 AAI shows a modest scan angle dependence not caused by instrument degradation This is another intrinsic property of the AAI Last but no
17. g Experiment 2 GOME 2 This instrument is designed to measure the total column and profiles of atmospheric ozone and the distribution of other key atmospheric constituents GOME 2 is a nadir viewing EUMETSAT O3MSAF sue REFERENCE O3MSAF KNMI PUM 002 1 50 2015 05 20 DATE 11 32 across track scanning spectrometer with a swath width of 1920 km It measures the radiance back scattered from the atmosphere and the surface of the Earth in the ultraviolet and visible range The instrument uses four channels to cover the full spectral range from 200 to 790 nm with a spectral sampling of 0 11 nm at the lower end of the range rising to 0 22 nm at the higher end The instrument employs a mirror mechanism which scans across the satellite track with a maximum scan angle that can be varied from ground control and three multi spectral samples per scan The ground pixel size of GOME 2 is 80 x 40 km for the shortest integration times but is usually 8 times larger for the detector measuring the shortest UV wavelengths Table 1 GOME 2 properties of MetOp A Spectrometer type double spectrometer w ith pre disperser prism and four holographic gratings Spectral range 240 790 nm Field of view 0 286 across track x 2 75 along track Entrance slit 0 2 mm across track x 9 6 mm along track 1a 203 306 nm 1b 306 322 nm Channels Bands amp 2a 290 399 nm sampling amp resolution 2b 299 412 nm 3 391 607 n
18. in this group the same as for the Geolocation group Table 6 Data group contents Quality Section Dataset name Data Description type Quality Input Int arr N A Quality flags for the input data 0 false 1 true rank Non nominal level 1 due to instrument degradation DEGRADED_INST_MDR in Level1b RD1 1 Non nominal level 1 due to processing degradation DEGRADED PROC MDR in Levelib RD1 2 Groundpixel is in SAA F SSA in Levelib PCD BASIG RD1 3 Sunfile of date missing older sunfile used 7 Earthshine radiance data missing 8 Earthshine radiance data invalid 9 Solar irradiance data missing 10 Solar irradiance data invalid 14 Failure in setup of the Forward Model Input REFERENCE O3MSAF KNMI PUM 002 1 50 W EUMETSAT O3MSAF sue DATE 26 32 16 Sunglint flag 17 not used 18 Cloud Pressure Adjusted to Surface Pressure 19 Other error 20 31 reserved for future use QualityProcessin Quality flags for processing 0 false 1 true 999 g rank No Retrieval done 1 value not initialized not used 2 0 5 not used 6 No retrieval done due to any kind of input errors 32 7 31 reserved for future use Output Section Dataset name Data Description type NElements ee Number of AAI elements per set rank 1 Absorbing Aerosol Index Dimension NElements x NSets Degradation Correction factor Residue values that were not corrected for degradation
19. itud e SubSatellitePointLatitude Longitude of the center of the ground pixel F Latitude of the center of the ground pixel F Longitude of corner A of the pixel Latitude of corner A of the pixel Solar zenith angle center of the ground pixel Solar Azimuth angle w r t north for center of ground pixel at HO LineOfSight zenith angle for center of the ground pixel Line of Sight Azimuth angle w r t north of the ground pixel Relative Azimuth angle between sun and viewing angles Geocentric longitude of subsatellite point Geodetic latitude of subsatellite point REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue HOEN DATE 24 32 Dataset name Data Description type L 8 ScanDirection N A Direction of the scan mirror 1 forward 2 backward ScannerAngle Angle of the scan mirror NrOfPixelsInScan Int arr N A Number of pixels within the scan line rank 2 NElements Int ar N A Number of pixels in each AAI set rank 2 IndexInScan Int ar N A Index of the pixel within the scan line This rank 2 indicates whether the pixel is a forward scan pixel indices 1 12 1 24 or backscan pixel indices 13 16 25 32 REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue a JE 5 1 5 Data Group The datasets in the Data group are given in Table 6 The data type and value of the Unit attribute are given for each dataset Attributes attached to all datasets
20. llite series is the core element of the EUMETSAT Polar System EPS developed in partnership with the European Space Agency It carries a complement of new European instruments as well as versions of operational instruments flown on the corresponding NOAA satellites of the USA The EUMETSAT programme includes provision for the development of the MetOp spacecraft in conjunction with the European Space Agency ESA the construction and launch of three new MetOp spacecraft the development of the corresponding instruments and ground infrastructure and provision for routine operations over a period of 15 years from the date of first launch This polar system is complementary to EUMETSAT s existing Meteosat satellites in geostationary orbit The EPS MetOp satellites MetOp A and MetOp B fly in a sun synchronous polar orbit at an altitude of about 840 km circling the planet 14 times each day and crossing the equator at 09 30 local sun time on each descending south bound orbit Successive orbits are displaced westward due to the Earth s own rotation giving global coverage of most parameters at least twice each day once in daylight and once at night The spacecraft carries a comprehensive set of instrumentation designed primarily to support operational meteorology and climate monitoring but also supporting many additional applications 3 2 GOME 2 METOP carries a number of instruments including the Global Ozone Monitorin
21. m 4 584 798 nm Polarisation monitoring unit 250 detector pixels 312 790 nm in 12 programmable bands spectral resolution 2 8 nm at 312 nmto 40 nm at 790 nm amp 0 14 0 11nm amp 0 24 0 29 nm amp 0 11 nm amp 0 13 nm amp 0 13 nm amp 0 22 nm amp 0 22 nm amp 0 24 0 29 nm amp 0 26 0 28 nm amp 0 26 0 28 nm amp 0 44 0 53 nm amp 0 44 0 53 nm Sw ath w idths 1920 km nominal mode 960 km 320 km 240 km 120 km Solar calibration Once per day Spectral calibration fixed angle once per day to once per month White Light Source fixed angle night side of the orbit Dark signal Default spatial Band 1a 640 km x 40 km 1920 km sw ath and integration time of 1 5 s resolution and Band 1b 4 80 kmx 40 1920 km sw ath and int time of 0 1875 s integration time PMD 10 km x 40 km for polarisation monitoring REFERENCE O3MSAF KNMI PUM 002 i 1 50 EUMETSAT O3MSAF sue DATE 12 32 4 ALGORITHM BACKGROUND 4 1 Absorbing Aerosol Index The Absorbing Aerosol Index AAI indicates the presence of elevated absorbing aerosols in the troposphere like desert dust and smoke It separates the spectral contrast at two ultraviolet UV wavelengths caused by absorbing aerosols from that of other effects including molecular Rayleigh scattering surface reflection gaseous absorption and aerosol and cloud scattering The AAI emerged as an error estim
22. n products from the satellite measurements 2 3 Product families Near real time Total Column NTO 03 NO2 O3Tropo NO2Tropo Near real time Ozone Profile NOP Near real time UV Index NUV REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue er DATE 9 32 Offline Total Column OTO 03 NO2 O3Tropo NO2Tropo SO2 BrO H2O HCHO OCIO Offline Ozone Profile OOP Offline Surface UV OUV Aerosols ARS 2 4 Product timeliness and dissemination Data products are divided in two categories depending on how quickly they are available to users Near real time products are available in less than three hours after measurement These products are disseminated via EUMETCast NTO NOP GTS NTO NOP or Internet NUV Offline products are available in two weeks from the measurement and they are archived at the O3MSAF archives in Finnish Meteorological Institute OOP OUV ARS and German Aerospace Center OTO Only products with pre operational or operational status are disseminated Up to date status of the products and ordering info is available on the O3MSAF website 2 5 Information Information about the O3MSAF project products and services http o3msaf fmi fi O3MSAF Helpdesk o3msaf fmi fi EUMETSAT O3MSAF ssu 3 METOP AND GOME 2 3 1 MetOp MHS DCS ARGOS relay antennas 5 y REFERENCE O3MSAF KNMI PUM 002 1 50 2015 05 20 DATE 10 32 The MetOp sate
23. ng zero or small negative residues The residue is sensitive to sunglint which should be flagged Sunglint is expected in GOME 2 data at the east side of the swath REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue er ATE p The residue is very sensitive to the absolute radiometric calibration of satellite radiances at 340 and 380 nm RD1 Deviations in the residue due to calibration errors may be presents in the level 1B data The residue or AAI in case of GOME 2 ranges typically from about 1 for cloudy scenes to 2 and larger for desert dust or smoke plumes 4 3 Level 1 Input The basic level 1B data consists of a calibrated solar spectrum and spectra of calibrated geo located radiances each spectrum comes with a wavelength grid error estimates and status flags In the geolocation record solar and line of sight viewing angles are specified at the spacecraft satellite height and earth radius are specified for the sub satellite point and for each nadir view footprint the centre co ordinates surface latitude and longitude are given The spectral level 1b data used in the calculation of the AAI are 1 nm averaged reflectances at 340 and 380 nm 4 4 Level 2 output Aerosol data are calculated and written as one or more HDF5 product files per orbit The product contains the geolocation angles and the retrieved AAI At a later stage the other aerosol parameters will be added to the product as they come availabl
24. o users user aCCESS r rrrrrnrrnnrnnnnnnnnnrrnovnnrvrnrvnnnrnnnnnnrnnrrnrrsrrnnrnnnnnnr 14 4 6 Geographical coverage and Granularity of the level 2 product 0sceeeeeeees 14 5 THE ARS AAI PRODUCT ra sisssivoscsccescnscascecdetieniccceidescceevascenctetawcesvsevciuidseceinveavecsnsneds 16 5 1 Structure of the ARS Product File sj vicciet ee cihaciies ahaha lined ad ddadcenent 16 5 4 1 Metadata Gosaasaarsemr sperret 17 5 1 2 Product Specilic Metadata Group usassmsensmikkuuemmnii hud e 22 5 1 3 GL 9 EE 90 aaa 22 5 1 4 Geolocation Giss vvs osn ee 22 51 9 Data Geek 25 EAT 27 5 3 File name convention rrrrnranranrvnrrnvrnrrnrrnrrnnrnnnnnnnnnnnnnnnnnnnnnnnnnnenennannennennennennennennene 27 REFERENCE O3MSAF KNMI PUM 002 i 1 50 amp EUMETSAT O3MSAF sue 2015 05 20 DATE 5 32 5 4 File size estimate rrrrnnnrrrrrrvrrrrnnnnrrvvrrvrnnnnnnrrrnnnnnnnnnsreennnnnnnenrernnrnnnernsssnennnnnnnnsnennn 27 5 4 1 Estimated size of ARS output file eerrnrnnornrnonnnnrnrnrrrrnrennnnennrnrnnnrnnnnnnrnrnnnene 27 EE gt 0 the data RE ER eee re ere ETE EEE ener 28 EEE EE E ee eee 28 FEET EE EE 28 5 5 EST Ga Flag RE eiiean iE eRe PeR Ear EE EEEa Ei Eaa TEER 29 5 5 4 ScaterngAngle uuaes eusesaunsjndaavdnnemviteitieurennevvkdnb inline 29 6 PRODUCT QUALITY AND CHARACTERISTICS runnevrrnnnvvnnnnnvvvnnnnnvnenennnennnnnnnnr 30 7 FURTHER INFORMATION siscescaccescsccacesccuiissheccesdesdesacenvencessenteerentca
25. ound pixel geometry The calculated results are stored in the Data group It contains information about the quality of the retrieval auxiliary information the definition of the state vector and the retrieval results Because the output product contains information for series of pixels all information in the Data and Geolocation group is organized in multi dimensional arrays The first dimension always corresponds to the total number of pixel sets which has been processed hereafter referred to as NSets the total number of retrievals per set is referred to as NElements f a value could not be calculated a fill value is written to the array as a placeholder indicating no data in contrast to invalid data Each array has five attributes Title Unit FillValue ValidRangeMin and ValidRangeMax which are used to describe the contents of the array 5 1 1 Metadata Group The content of the Metadata group is shown in the following table The allowed values for the parameters which are required by UMARF are consistent with the requirements given in Table 2 The allowed values given in italics mean any value of the given type e g string means that the attribute can contain any string within the UMARF size limit REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sse o ea DATE 18 32 Table 2 Metadata group contents Attribute name Data Description Allowed values Type SatellitelD string Platform identifier mission and
26. ps Metadata Product Specific Metadata Geolocation and Data see Figure 1 The values in all groups are taken either from the level 1b or other input data files copied from the configuration file or calculated by the program mg die filename h5 METADATA PRODUCT SPECIFIC METADATA Eal GEOLOCATION Cy DATA Figure 1 Structure of the HDF5 file The Metadata group contains parameters about the satellite instrument required by UMARF such as metadata given in the O3MSAF software requirements the scanning mode the algorithm version and other general information about the product The Product Specific Metadata group is reserved for additional information specific to this product e g parameters related to the algorithm which has been used to generate the product All values in the Metadata and Product Specific Metadata groups are stored as attributes The geolocation information of each ground pixel can be found in Geolocation group It contains all information such as corner and center coordinates See Figure 2 and Figure 3 for the definition of the seven points of the ground pixel Wd y lt 0 w d gt 0 ground O ho flight direction forward scan 187 5 ms groundpixel A c B Q REFERENCE O3MSAF KNMI PUM 002 i 1 50 EUMETSAT O3MSAF sue HoN DATE 17 32 Figure 2 Ground pixel geometry _ Flight Direction Scan Direction Earth Surface Figure 3 Gr
27. spacecraft the product originated from OrbitType string Coverage of the product global local StartOrbitNumber int First of the two orbit numbers in the EPS product valid at the star of sensing i e at the beginning of a dump InstrumentID string Instrument which acquired the product InstrumentMode string Scanning mode NORTH POLAR VIEW of the instrument SOUTH POLAR VIEW at the time of the NARROW VIEW acquisition NORMAL VIEW STATIC VIEW UNKNOWN SensingStartTime String 23 UTC date and Date in CCSDS format time at acquisition start of the product SensingEndTime String 23 UTC date and Date in CCSDS format time at acquisition end of the product ReceivingCentre string Centre that String received the data ProcessingCentre string 5 Centre that O3KNM or other String generated the data ProcessingMode string 1 N ominal Backlog string 2 String 23 string 4 string 4 ProcessingLevel ProcessingTime BaseAlgorithmVersion ProductAlgorithmVersion ParentProducts ProductFormatType string Data format of the HDF5 product ProductType ProductFormatVersion SubSatellitePointStartLat REFERENCE O3MSAF KNMI PUM 002 EUMETSAT O3MSAF ssu DATE applied for generation of the product Processing level applied for generation of the product UTC date and time at processing end of the product Version of the algorithm which was us
28. t least at the east side of the swath at high latitudes both North and South there are areas showing too large values for the AAI This is known behaviour of the AAI product These data should not be used or at least treated with caution REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue er DATE 32 32 7 FURTHER INFORMATION 7 1 O3MSAF website Further up to date information and documentation on the ARS aerosol products should be available from the O3MSAF website http 03msaf fmi fi Requests for data and questions with regards to O3MSAF products should be directed to the user services Contact information is also available on the website mentioned above 7 2 User Notification Service EUMETSAT maintains a User Notification Service UNS that disseminates instantaneous messages relating to the platform MetOp A the GOME 2 instrument and derived L1 and L2 products and weekly notifications of upcoming ground segment and SAF related scheduled maintenance activities The SAF recommends that Near Real Time users subscribe to this notification service at least the instrument related and weekly notifications This ensures also that the SAF has a channel to notify users of upcoming changes in the L2 format and or quality of the products 7 3 Acknowledgement instructions When O3MSAF data is used for operational or scientific purposes the source of this data should be acknowledged For example The data of the
29. thm Theoretical Basis Document ECMWF European Centre for Medium range Weather Forecast ERS European Remote Sensing Satellite ESA European Space Agency EUMETSAT European Organisation for the Exploitation of Meteorological Satellites FRESCO Fast Retrieval Scheme for Cloud Observables FWHM Full Width Half Maximum GDP GOME Data Processor GOME Global Ozone Monitoring Instrument KNMI Royal Netherlands Meteorological Institute LUT Look Up Table REFERENCE O3MSAF KNMI PUM 002 i 1 50 EUMETSAT O3MSAF sse DATE 7 32 O3MSAF Satellite Application Facility on Ozone Monitoring OMI Ozone Monitoring Instrument OPERA Ozone Profile Retrieval Algorithm PMD Polarization Measurement Device PUM Product User Manual RMS Root Mean Square RTM Radiative Transfer Model SAF Satellite Application Facility SCI SCattering Index SZA Solar Zenith Angle TOMS Total Ozone Mapping Spectrometer UV Ultra Violet VIS Visible 1 4 Reference documents RD1 RD2 RD3 Algorithm Theoretical Basis Document for ARS version 2 2 dd 2013 06 16 de Graaf M P Stammes O Torres and R B A Koelemeijer 2005 Absorbing Aerosol Index Sensitivity analysis application to GOME and comparison with TOMS J Geophys Res 110 D01201 doi 10 1029 2004JD005178 O3MSAF Validation Report of the Absorbing Aerosol Index products SAF 03M KNMI VR 001 issue 3 2013 2013 06 11 REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF su
30. tion for instrument degradation is not applied in the current data version As for the quality of the ARS AAI products it has been studied using a number of different verification techniques An extended report of these studies and their results may be found in the O3M SAF Validation Report Here we summarise the main conclusions 1 Global maps of GOME 2 AAI compare well to global maps of OMI AAI 2 From a pixel to pixel comparison with the AAI from SCIAMACHY it is found that the GOME 2 MSC AAI is of good quality This we conclude from the good one to one correlation between GOME 2 and SCIAMACHY AAI The offset between the GOME 2 MSC AAI and SCIAMACHY AAI is found to be close to zero Additionally the bias corrected uncertainty in the GOME 2 MSC AAI was found to be 0 5 index point This is only an upper limit because this value is also determined by the quality of the SCIAMACHY AAI and the performance of our intercomparison approach In any case the bias corrected value of 0 5 index points relates well to the target uncertainty of 0 5 index points mentioned in the PRD 3 More quantitative results follow from the analyses of the global mean residue The global mean MSC residue in particular revealed a similar seasonal variation for GOME 2 on MetOp A as was found earlier for GOME 1 However a modest offset of 0 4 index points w r t the GOME 1 global mean value was found When the calculation was repeated taking only those measur
31. uenseeceureeeseenees 32 TONER WE SNS AEE 32 7 2 User Notification Service air 32 7 3 Acknowledgement instructions sessssesseeseesneerrt rrr rrrrerttttrerretrssrssttsnrt nn rtnrrttnennnt 32 REFERENCE O3MSAF KNMI PUM 002 1 50 EUMETSAT O3MSAF sue DATE 6 32 1 INTRODUCTION 1 1 Purpose This document is the Product User Manual for the Offline ARS aerosol products retrieved within the context of the Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring O3MSAF This document first presents some background information and a brief description of the retrieval algorithm Next the document provides information and guidance to the user on howto use and interpret the data product 1 2 Scope This PUM provides information on the ARS product of the O3MSAF This document does not go into much detail with regards to the algorithm or design of the software please refer to the Algorithm Theoretical Basis Document ATBD for that information As the instruments go through phases of degradation the product quality is affected This Product User Manual does not describe the product quality beyond an initial demonstration of the output For monitoring the product quality of the aerosol products the reader is referred to the O3MSAF Validation Report on the Aerosol products SAF O3M KNMI VR 001 1 3 Glossary 1 3 1 Acronyms AAI Absorbing Aerosol Index ARS Aerosol Retrieval System ATBD Algori
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