2.3.1 spase://NASA/NumericalData/SES-14/GOLD/L2/TLIMB/PT8S Gold Level L2 exospheric temperature 2020-07-07T21:15:18Z GOLD retrieves the exospheric temperature from the integrated N2 LBH radiance profile obtained from atmospheric limb scans (LIM observation mode). This data product, referred to as TLIMB, is derived from limb scan data by fitting the shape of the LBH radiance profile between 100 and 300 km. Algorithm heritage An approach similar to the GOLD TLIMB retrieval has been used to analyze data from TIMED/GUVI, Cassini/UVIS and MAVEN/IUVS. The GOLD TLIMB algorithm is most similar to the operational algorithm used to retrieve exospheric temperature on Mars from MAVEN/IUVS CO2 density retrievals. The GOLD algorithm follows the procedure outlined in Lo et al. [2015] as originally applied to the atmosphere of Mars. The operational code is implemented in IDL and has been generalized to be used with any species in any planetary atmosphere. Algorithm theoretical basis Limb profiles of thermospheric airglow emissions depend fundamentally on temperature, particularly the decay rate with altitude above the peak of the emission. This has been exploited in retrieval algorithms for analyzing far-ultraviolet limb emissions from low-Earth orbit (e.g., Picone and Meier [2000]). For GOLD, the low spatial resolution on the limb mandates that, rather than attempting to fit an entire temperature profile, we only infer a single parameter, the exospheric temperature (TLIMB), defined as the temperature of the atmosphere when in diffusion equilibrium. We use daytime, non-auroral N2 LBH emission limb brightness profiles where the only excitation mechanism is photoelectron impact on N2. LBH emission bands in the 137-160 nm range are integrated spectrally, excluding the N I 149.3 nm line. The GOLD limb scan measurements are done in one hemisphere at a time, and the L1C LIMB data covers a latitude range from the equator to ~20 degree. The specific steps involved in the TLIMB retrieval are as follows: • Filter data using topside tangent height range (~100-300 km). • Fit a Chapman function to the emission brightness profile. • Obtain the N2 scale height H (Zo) from the Chapman fit. • Obtain T∞ from H (Zo) = kT/Mg, where k is Boltzmann’s constant, M is the molecular mass of N2, and g is the gravitational acceleration. Note that this fit is independent of the absolute brightness calibration of the airglow intensity, it depends only on the shape of the radiance profile. For this reason, it is necessary to detect stars in the field-of-view, since the emission from stars can produce a profile shape that can be very different from a profile produced solely by thermospheric airglow. References Picone and Meier (2000), Similarity transformations for fitting of geophysical properties: Application to altitude profiles of upper atmospheric species, J. Geophys. Res., 105, 18599, doi:10.1029/1999JA000385]. Lo, D. Y., et al. (2015), Nonmigrating tides in the Martian atmosphere as observed by MAVEN IUVS, Geophys. Res. Lett., 42, 9057–9063, doi:10.1002/2015GL066268. Snowden, D., R. V. Yelle, J. Cui, J.-E. Wahlund, N. J. T. Edberg, and K. Ågren (2013), The thermal structure of Titan’s upper atmosphere, I: Temperature profiles from Cassini INMS observations, Icarus, 226, 52–582. National Aeronautics and Space Administration; Dr. Richard Eastes spase://SMWG/Person/Richard.Eastes PrincipalInvestigator spase://SMWG/Person/James.M.Weygand MetadataContact GOLD Homepage web page https://gold.cs.ucf.edu/ GOLD web page with news and other information. GOLD Missions Space Science Reviews Article https://doi.org/10.1007/s11214-017-0392-2 Eastes, R.W., McClintock, W.E., Burns, A.G. et al. Space Sci. Rev. (2017) vol. 212, pp.383. spase://VSPO/NumericalData/SES-14/GOLD/L2/TLIMB/PT8S spase://SMWG/Repository/NASA/GSFC/SPDF Online Open FTPS from SPDF (not with most browsers) ftps://spdf.gsfc.nasa.gov/pub/data/gold/level2/ FTPS access to Gold Level L2 data HTTPS from SPDF https://spdf.gsfc.nasa.gov/pub/data/gold/level2/ HTTPS access to Gold Level L2 data NetCDF Space Physics Data Facility of the NASA Goddard Space Flight Center; Robert E McGuire Calibrated GOLD Gold Level L2 Exospheric Temperature Level 2 1 spase://SMWG/Instrument/SES-14/GOLD ImageIntensity 2018-10-06T00:00:00 P1D PT8S Earth.NearSurface.Ionosphere O relative to N2 GOLD SES-14 Model Uncertainty in Exospheric Temperature tdisk_unc_mod Model uncertainty in retrieved exospheric temperature. PT8S K 0 1000 9.9692e+36 Uncertainty Other Random Uncertainty in N2 LBH n2_lbh_unc_ran Random uncertainty in LBH slant path radiance. PT8S Rayleighs 0 100000 9.9692e+36 Photon Uncertainty Intensity Random Uncertainty in LBH Scale Height n2_scale_height_unc_ran Random uncertainty in top side LBH scale height. PT8S km 0 2 9.9692e+36 Uncertainty Other Exospheric Temperature tlimb Retrieved exospheric temperature. PT8S K 0 100000 9.9692e+36 Molecule Temperature 14 Mask Wavelength mask_wavelength Wavelength grid for N2_LBH mask. PT8S nm 130 170 9.9692e+36 Photon Scalar Wavelength Channel channel GOLD channel (‘A’ or ‘B’). PT8S Scalar Other TLimb Quality Flag tlimb_dqi TLimb data quality index per pixel (GOLD Public Science Data Products Guide). PT8S 0 2147483647 -2147483647 Scalar Other Systematic Uncertainty in LBH Scale Height n2_scale_height_unc_ran Systematic uncertainty in retrieved exospheric temperature. PT8S km 0 2 9.9692e+36 Uncertainty Other Tangent Point Latitude tangent_point_latitude Latitude at each tangent point. PT8S degrees -90 90 9.9692e+36 Direction Positional Systematic Uncertainty in Exospheric Temperature tlimb_unc_sys Systematic uncertainty in retrieved exospheric temperature. PT8S K 0 10000 9.9692e+36 Photon Uncertainty Intensity Random Uncertainty in Exospheric Temperature tlimb_unc_ran Random uncertainty in retrieved exospheric temperature. PT8S K 0 10000 9.9692e+36 Photon Uncertainty Intensity Overall Quality Flag dqi TLIMB data quality index (GOLD Public Science Data Products Guide). PT8S 0 2147483647 -2147483647 Scalar Other Scan Start Time scan_start_time UTC start time of scan, e.g., "2017-06-21T23:46:38.015Z". PT8S date/time ' ' Magnitude Temporal TLimb Lookup Table tlimb_lookup_table Retrieval lookup table filename. PT8S Other Solar Zenith Angle tangent_point_solar_zenith_angle Solar zenith angle at each tangent point. PT8S degrees 0 180 9.9692e+36 Direction Positional Tangent Point Longitude tangent_point_longitude Longitude at each tangent point. PT8S degrees -180 180 9.9692e+36 Direction Positional Systematic Uncertainty in LBH Slant Path Radiance n2_lbh_unc_sys Systematic uncertainty in LBH slant path radiance. PT8S Rayleighs 0 100000 9.9692e+36 Uncertainty Other UTC time time_utc UTC date/time string: "2017-06-21T23:46:38.015Z". PT8S date/time ' ' Scalar Temporal Top Side Scale Height of LBH Profile n2_scale_height Top side scale height of N2 LBH radiance profile. PT8S km 15 30 9.9692e+36 Scalar Other L1C File Name input_l1c_file L1C file name for each occultation. PT8S ' ' Scalar Other N2 LBH brightness radiance_n2_lbh N2 LBH brightness used in retrieval. PT8S Rayleighs 0 100000 9.9692e+36 Photon Scalar Intensity Tangent Point Altitude tangent_point_altitude Tangent point altitude at each latitude/longitude grid point. The size of the data array varies with the number of stellar occultations. PT8S km 0 1000 9.9692e+36 Direction Positional Model Uncertainty in LBH Scale Height n2_scale_height_unc_mod Model uncertainty in top side LBH scale height. PT8S km 0 2 9.9692e+36 Uncertainty Other Scan Stop Time scan_stop_time UTC stop time of scan, e.g., "2017-06-21T23:46:38.015Z". PT8S date/time ' ' Magnitude Temporal Mask Defining LBH Bandpass mask_n2_lbh Wavelength mask defining LBH bandpass used in retrieval. PT8S 0 1 -2147483647 Other Hemisphere Scanned hemisphere Hemisphere scanned (‘N’ or ‘S’). PT8S ' ' Scalar Other