Venus Climate Orbiter Akatsuki IR2 Level 3 data set =================================================== Releases -------- release of vcoir2_7001 Release Date: 2019-06-28 Data Coverage: 2010-12-09 -- 2016-12-09 Data sets used to create this data set: - VCO-V-IR2-3-CDR-V1.0 https://doi.org/10.17597/isas.darts/vco-00009 - VCO-V-IR2-3-SEDR-V1.0 https://doi.org/10.17597/isas.darts/vco-00010 - VCO-V-SPICE-6-V1.0 https://doi.org/10.17597/isas.darts/vco-00001 Data Citation ------------- The citation for this data set is as follows: Murakami, S., K. Ogohara, M. Takagi, H. Kashimura, M. Yamada, T. Kouyama, T. Horinouchi, T. Imamura, Venus Climate Orbiter Akatsuki IR2 Longitude-Latitude Map Data v1.0, JAXA Data Archives and Transmission System, https://doi.org/10.17597/ISAS.DARTS/VCO-00018, 2018. Overview -------- This data set contains longitude-latitude map data created from images acquired by the IR2 instrument of the Venus Climate Orbiter (VCO, also known as PLANET-C and AKATSUKI) spacecraft. This data set consists of NetCDF and FITS files. The longitude-latitude map data are included as Level 3 product in NetCDF. During process of creating longitude-latitude map data, pointing of spacecraft was corrected using limb-fitting technique. Detected limb points and information on fitted ellipse are provided as auxiliary data, Level 3x product in NetCDF. Level 3x product in FITS is also provided, which can be used as geometry information file with poiting correction instead of "geo" file provided in VCO-V-IR2-3-SEDR-V1.0. This data set is produced from calibrated image, geometry information, and SPICE kernel data sets. Please refer VCO-V-IR2-3-CDR-V1.0, VCO-V-IR2-3-SEDR-V1.0, and VCO-V-SPICE-6-V1.0 data sets for detailed information on the instrument and acquired data. Processing ---------- Overview -------- The data processings are done on DANS (Data Analysis Network System) managed by C-SODA (Center for Science-satellite Operation and Data Archive), ISAS/JAXA at Sagamihara, Kanagawa, Japan. Note that DANS consists of SIRIUS (Scientific Information Retrieval and Integrated Utilization System), EDISON (Engineering Database for ISAS Spacecraft Operation Needs), "Reformatter", DARTS (Data ARchives and Transmission System) and data analysis servers. The summary of the data processing is as follows. The data downlinked as telemetry are transferred to the data accumulation system at ISAS, and are registered to SIRIUS and are sorted in time. From SIRIUS, level 0 data are retrieved to the Reformatter for the PLANET-C Project Team that is provided by C-SODA to each mission. All processings (data pipeline) after level 0 until level 3 are done on the Reformatter. These procedures are executed automatically. To implement these procedures, various program codes are used, written in C, C++, Fortran 90/95, Ruby, Python, Perl, and POSIX shell. Definition of Products ---------------------- Definition of products is as follows: abbr name description ----- ------------ ------------------------------------------------- l3b Level 3b calibrated, physical values projected onto equally spaced longitude-latitude grid derived from l2b data with pointing correction using limb-fitting technique. l3bx Level 3b aux data for evaluation of automated limb-fitting and pointing corrected data product, l3b. l3bx can be used instead of geometry information product, "geo", provided as VCO-V-IR2-3-SEDR-V1.0 that is calculated using only SPICE kernels, VCO-V-SPICE-6-V1.0. Detailed description of the processings --------------------------------------- From L2b FITS file, L3b NetCDF file, and L3bx NetCDF file are created using SPICE kernels and SPICE toolkits. The fully-automated algorithms of limb-detection, limb-fitting and interpolation onto equally spaced longitude-latitude grids has been implemented for the processing. For verification of the result of limb-detection and limb-fitting, L3bx NetCDF file is also created. This file also contains correction of pointing of the camera. Using the correction of pointing of camera, L3bx FITS file is created. L3bx FITS file has a similar structure to geometry information file ("geo" file), so one can use L3bx FITS file as pointing-corrected geometry information file instead of geometry information file created at the L1b data processing. See Ogohara et al. (2017), Ogohara et al. (2012), and doc/vco_l3_algorithm_v${VV}.pdf for detailed description of algorithms and processings, where ${VV} is zero-padded two-digit version number. Data ---- Overview -------- There are three kinds of images, L3b NetCDF file, L3bx NetCDF file, and L3bx FITS file. Each L3b NetCDF file corresponds to L3bx NetCDF file that has same filename except for the abbreviation of "product" part, e.g., "l3bx" instead of "l3b". Each L3bx NetCDF file corresponds to L3bx FITS file that has same filename except for the extension, e.g., ".fit" instead of ".nc". File format and structure ------------------------- The files with the extension ".nc" under "data" directory are NetCDF-4 file. These NetCDF files are considered to be compliant with the CF convention (CF Version CF-1.7). Compliance to CF-1.7 is verified as no "Errors" using following conditions: - CF Checker Version 3.1.0 (https://github.com/cedadev/cf-checker), - Using Standard Name Table Version 67 (2019-06-18T13:25:38Z), - Using Area Type Table Version 9 (07 August 2018), - Using Standardized Region Name Table Version 4 (18 December 2018). In L3b NetCDF file, there is "radiance" variable which is a function of "longitude", "latitude", and "time" variables. In L3bx NetCDF file, there is "radiance" variable which is a function of "axis1", "axis2", and "time" variables. For these two kinds of NetCDF files, the "time" variable has only one value of the representative observation time in hours since 2000-01-01T00:00:00 UTC. Other variables are described doc/vco_l3_variable_v${VV}.pdf where ${VV} is zero-padded two-digit version number. The "axis1" and "axis2" are position of the full-size image coordinate that is defined in document/imagecoord.txt file of VCO-V-IR2-3-SEDR-V1.0 dataset. The files with the extension ".fit" under "data" directory are FITS format file. These FITS files are considered to be compliant with the FITS Standard Version 4.0 published online on 22 July 2016 by the IAUFWG except for handling of keywords that stores numeric value. If value of the keyword is supposed to be ``Not Available'', the value is set to 'N/A' in string literal in spite of definition of the keyword that stores numeric value. This is a work around for non-existence of numeric literals that represent special values in FITS Standard Version 4.0. For each L3bx FITS file, each data is stored in the data part of the several HDUs (Header Data Unit). The list of HDU in the files is as follows: HDU 0: Primary HDU (header only) HDU 1: IMAGE extension, Latitude HDU 2: IMAGE extension, Longitude HDU 3: IMAGE extension, Local (Solar) Time HDU 4: IMAGE extension, Phase Angle HDU 5: IMAGE extension, Incidence Angle HDU 6: IMAGE extension, Emission Angle HDU 7: IMAGE extension, Azimuthal Angle HDU 8: BINTABLE (Binary Table) extension, lpxf and lpyf HDU 9: BINTABLE (Binary Table) extension, lpxm and lpym HDU 10: BINTABLE (Binary Table) extension, epx and epy HDU 11: IMAGE extension (header only) There are pointing-corrected geometry information. These files have same HDU structure as "geo" file provided in the VCO-V-IR2-3-SEDR-V1.0 data set up to the HDU 7. Each file can be used as improved version of geometry information file that has same filename except for the abbreviation of "product" part, e.g., "l3bx" instead of "geo". For definitions of each data array for the HDUs from 0 to 7, see "catalog/dataset.cat" in the VCO-V-IR2-3-SEDR-V1.0 data set. In the HDU 8, 9, and 10, (lpxf, lpyf), (lpxm, lpym), and (epx, epy) variables in L3bx NetCDF file are stored, respectively, in BINTABLE (Binary Table) extension. In the HDU 11, there are other variables stored in L3bx NetCDF file. Filename -------- File under browse and data directories has the following filename format: ${cam}_${YYYYMMDD}_${hhmmss}_${filter}_${product}_v${ver}.${ext} where ${cam}: abbreviation of the instrument, ir2. ${YYYYMMDD}: observation date, YYYY is year, MM is month, and DD is day. ${hhmmss}: observation time, hh is hour, mm is minute, and ss is second. ${filter}: abbreviation of the filter, 174, 202, 226, and 232. ${product}: abbreviation of the product, l3b and l3bx. ${ver}: version of the product, 10. ${ext}: extension of the file, nc, fit, png, and jpeg. Text dump of header of NetCDF file has similar filename format: ${cam}_${YYYYMMDD}_${hhmmss}_${filter}_${product}_v${ver}_header.txt Directory Structure ------------------- Directory structure is as follows: 00readme.txt this file checksum.txt list of MD5 checksum browse/ browsing directory browse/${prd}/ product directory browse/${prd}/${t}/ file type directory browse/${prd}/${t}/list.html HTML file for browsing browse/${prd}/${t}/${PVVVV}/ orbit number string directory browse/${prd}/${t}/${PVVVV}/list_*.html HTML file for browsing browse/${prd}/${t}/${PVVVV}/*.png PNG image of data file browse/${prd}/${t}/${PVVVV}/*.jpg JPEG image of data file data/ directory for data data/${prd}/${t}/ directory for each file type data/${prd}/${t}/${PVVVV}/ orbit number string directory data/${prd}/${t}/${PVVVV}/*.nc NetCDF file data/${prd}/${t}/${PVVVV}/*.fit FITS file doc/vco_l3_algorithm_v${VV}.pdf description of algorithm used to create products in this data set doc/vco_l3_variable_v${VV}.pdf description of variable stored in L3 and L3x NetCDF file where ${prd}: abbreviation of the product, l3b and l3bx. ${t}: file type of data, netcdf and fits. ${PVVVV}: orbit number string directory (see below). ${VV}: version of the file. In 'data/' and 'browse/' directories, there are subdirectories with orbit number string as its name. The orbit number string is defined as PVVVV format, where 'P' indicates period before the successful orbit insertion ('c', the first character of 'cruise') or after the successful orbit insertion, i.e., orbiting phase ('r', the first character of 'revolution'). 'VVVV' indicates orbit number that is represented by zero-padded 4 digits. For the period before the successful orbit insertion, we assign the orbit number '0000', therefore, the orbit number string is 'c0000'. For orbiting phase, the orbit number begins from '0001', and it is incremented when the spacecraft passes the periapsis. So we'll have the orbit number strings, 'c0000', 'r0001', 'r0002', and so on. The orbit numbers for the VCO spacecraft are defined in '/extras/orbnum/vco_vVV.orb' of the VCO-V-SPICE-6-V1.0 data set, where VV is the version number of the orbit number file. License ------- This data set is distributed under "ISAS Data Policy" (*1). Rules described in the policy follow "Government of Japan Standard Terms of Use (Version 2.0)" (*2) and are compatible with Creative Commons Attribution 4.0 International License (CC BY 4.0) (*3). (*1) https://www.isas.jaxa.jp/en/researchers/data-policy/ (*2) https://www.kantei.go.jp/jp/singi/it2/densi/kettei/gl2_betten_1_en.pdf (*3) https://creativecommons.org/licenses/by/4.0/deed.en References ---------- Ogohara, K., M. Takagi, S. Murakami, T. Horinouchi, M. Yamada, T. Kouyama, G. L. Hashimoto, T. Imamura, Y. Yamamoto, H. Kashimura, N. Hirata, N. Sato, A. Yamazaki, T. Satoh, N. Iwagami, M. Taguchi, S. Watanabe, T. M. Sato, S. Ohtsuki, T. Fukuhara, M. Futaguchi, T. Sakanoi, S. Kameda, K. Sugiyama, H. Ando, Y. J. Lee, M. Nakamura, M. Suzuki, C. Hirose, N. Ishii, T. Abe, Overview of Akatsuki data products: definition of data levels, method and accuracy of geometric correction, Earth, Planets and Space, 69, 167, https://doi.org/10.1186/s40623-017-0749-5, 2017. Ogohara, K., T. Kouyama, H. Yamamoto, N. Sato, M. Takagi, T. Imamura, Automated cloud tracking system for the Akatsuki Venus climate orbiter data, Icarus, 217, 661-668, https://doi.org/10.1016/j.icarus.2011.05.017, 2012.