MIGHTI samples the O2 A band spectral region at five different wavelengths in order to both measure the shape of the band and to specify a background radiance that is subtracted from the signal. The wavelengths of the filter passbands are selected to maximize the sensitivity to lower thermospheric temperature variations. The temperature measurement is accomplished by a multichannel photometric measurement of the spectral shape of the molecular oxygen A-band around 762 nm wavelength. For each field of view, the signals of the two oxygen lines and the A-band are detected on different regions of a single, cooled, frame transfer charge coupled device (CCD) detector. Two filter channels sample either end of the band to define a background (754.1 nm and 780.1 nm) and three more sample its shape (760.0 nm, 762.8 nm and 765.2 nm). Using three filters that sample the band shape allows the simultaneous retrieval of the atmospheric temperature and common shifts in the center wavelengths of the pass bands due to thermal drifts of the filters. On-board calibration sources are used to periodically quantify thermal drifts, simultaneously with observing the atmosphere.
Version:2.6.0
MIGHTI samples the O2 A band spectral region at five different wavelengths in order to both measure the shape of the band and to specify a background radiance that is subtracted from the signal. The wavelengths of the filter passbands are selected to maximize the sensitivity to lower thermospheric temperature variations. The temperature measurement is accomplished by a multichannel photometric measurement of the spectral shape of the molecular oxygen A-band around 762 nm wavelength. For each field of view, the signals of the two oxygen lines and the A-band are detected on different regions of a single, cooled, frame transfer charge coupled device (CCD) detector. Two filter channels sample either end of the band to define a background (754.1 nm and 780.1 nm) and three more sample its shape (760.0 nm, 762.8 nm and 765.2 nm). Using three filters that sample the band shape allows the simultaneous retrieval of the atmospheric temperature and common shifts in the center wavelengths of the pass bands due to thermal drifts of the filters. On-board calibration sources are used to periodically quantify thermal drifts, simultaneously with observing the atmosphere.
| Role | Person | StartDate | StopDate | Note | |
|---|---|---|---|---|---|
| 1. | PrincipalInvestigator | spase://SMWG/Person/Brian.J.Harding | |||
| 2. | MetadataContact | spase://SMWG/Person/James.M.Weygand |
ICON spacecraft Homepage.
Space Science Reviews, 212(1-2), pp.553-584. DOI: 10.1007/s11214-017-0358-4
Web Service to this product using the HAPI interface.
Access to Data in NetCDF Format via https from SPDF
Access to NetCDFs via NASA/GSFC CDAWeb
This variable contains the time corresponding to the temperature profiles reported in this file. The variable is in milliseconds since 1970-01-01 00:00:00 UTC at middle of image integration. A human-readable version of the time can be found in the variable ICON_...UTC_Time.
Quality Flag indicating an inappropriate calibration file has been used or was missing.
Quality Flag indicating that the spacecraft is within the South Atlantic Anomaly (0 = not in SAA).
Derived common scaling of O2 A Band radiances in the 3 signal channels by altitude. Calculated forward radiances are fit to the observations from each of the three signal channels. The scaling is done at each tangent altitude separately and interatively until a best fit solution is found. The intensity of each signal channel relative to the other two determines the temperature, so the scale factor is unitless. The scaling is derived using pre-calculated spectra from the HITRAN 2016 database.
Derived uncertainty (1-sigma) in derived common scaling of O2 A Band to emergent intensity by altitude.
Background Signal by filter by altitude and filter. This has been corrected for flatfield effects across the detector.
Derived slope of subtracted background. The slope of the background is saved here for diagnostic purposes. It is calculated by taking the difference of the flatfielded signal from the two background channels and dividing by the difference of the the channel center wavelengths (in nm) of the two background channels (approximately 780 nm - 754 nm). This is done explicitly by [bg2 - bg1]/flatfield/[wavelength2 - wavelength1], where bg2 and bg1 are the observed background signals in electrons.
Total boresight to sun angle.
Field of view azimuth angle.
Filter Center Wavelength used in temperature retrieval (=1e7/FilterCWN).
Filter Center Wavenumber used in temperature retrieval as measured in the laboratory and fitted by a Gaussian. These filter center wavenumbers vary with detector (MIGHTI A and MIGHTI B), with altitude as well as with channel. They are also difference for daytime and nighttime operations. It is from these center wavenumbers that the common wavenumber shift (across all channels) is calculated.
Wavelength labels corresponding to the five filters. These are for guidance. Actual values used in retrieval for MIGHTI-A and MIGHTI-B (day/night) are in ICON_L23_MIGHTI_(A or B)_Filter_Center_Wavelength.
Common shift of all filter center wavenumbers due to thermal drift that is added to laboratory measured filter center wavenumbers. The three channels measuring the A band overdetermines the temperature such that the wavenumber registration due to any thermal drift of the instrument can be additionally inferred. This is typically fixed with altitude and determined (along with temperature) from the signal originating from the O2 A band as measured from 3 signal channels.
Uncertainties (1-sigma) in the shift of all filter center wavenumbers. If the common wavenumber shift is fixed with altitude and prescribed, then this uncertainty is zero everywhere.
Milliseconds since 1980-01-06 00:00:00 TAI (coincident with UTC) at middle of image integration. Derived from original GPS values reported from spacecraft (Time_GPS_Seconds and Time_GPS_Subseconds). Time calculation is offset by 615ms (flush time) for the first image in the series and for all other images are adjusted by subtracting (integration time + 308 milliseconds) from the reported GPS time.
The header of the first image received in a series 615 ms after start of image processing. Following headers are adjusted by subtracting (integration time + 308 ms) from the reported GPS time.
GPS Time in sub seconds, 50 nanosecond offset from GPS seconds from 20 MHz clock.
MIGHTI Integration Time in millieconds.
Observed relative radiance by filter and altitude. The retrieval is based on a forward modeling approach to these observed radiances as reported in electrons/s from the MIGHTI L1 product. These are converted to electrons based on the integration time during day (30 s) or night (60 s).
Uncertainty (1-sigma) in relative radiance by filter by altitude and filter. These are calculated by taking the square root of the total number of electrons in each of the three signal channels, which are 51 pixels wide for MIGHTI-A or MIGHTI-B (day or night).
Tangent point altitudes. These altitudes are the tangent altitude of the line of sight of each pixel.
Tangent point latitudes by altitude. Note that these are a function of both epoch and altitude. Note also that due to the nature of the limb observations these latitudes are typically an average over many hundreds of kilometers.
Local solar time (0-24 h) at tangent point calculated using the equation of time. LST is a function of both epoch and altitude.
Tangent point longitudes (0-360) by altitude. Note that these are a function of both epoch and altitude. Note also that due to the nature of the limb observations these longitudes are typically an average over many hundreds of kilometers.
Tangent point magnetic latitudes by altitude. Quasi-dipole latitude and longitude are calculated using the fast implementation developed by Emmert et al. (2010, doi:10.1029/2010JA015326) and the Python wrapper apexpy (doi.org/10.5281/zenodo.1214207). Quasi-dipole longitude is defined such that zero occurs where the geodetic longitude is near 285 deg east (depending on latitude). Note that these are a function of both epoch and altitude. Note also that due to the nature of the limb observations these latitudes are typically an average over many hundreds of kilometers.
Tangent point magnetic longitudes by altitude. Quasi-dipole latitude and longitude are calculated using the fast implementation developed by Emmert et al. (2010, doi:10.1029/2010JA015326) and the Python wrapper apexpy (doi.org/10.5281/zenodo.1214207). Quasi-dipole longitude is defined such that zero occurs where the geodetic longitude is near 285 deg east (depending on latitude). Note that these are a function of both epoch and altitude. Note also that due to the nature of the limb observations these longitudes are typically an average over many hundreds of kilometers.
Solar zenith angle at tangent point. SZA is a function of both epoch and altitude.
Derived temperatures from A band by altitude. Temperatures are retrieved from the rotational distribution of emission lines in the O2 A band. The measurement is made at 5 spectral channels. 3 channels measure the A band and 2 others on either side of the band measure a background, which is subtracted from the 3 signal channels. An entire altitude profile is observed simultaneously. An onion-peeling inversion is used on the raw observations to remove the effects of the integration along the line of sight. See Stevens et al. (Space Science Reviews (2018) 214:4. https://doi.org/10.1007/s11214-017-0434-9). O2 A band spectra are pre-calculated from 100-400 K in 20 K increments based on the HITRAN 2016 database [Gordon et al., JQSRT (2017), 203:3-69.https://doi.org/10.1016/j.jqsrt.06.038] and smoothed filter functions with FWHM of ~2.0 nm. The filter functions are based on Gaussian fits to laboratory measurements and are a function of channel, row (altitude), and column. The fits are separately done for each pixel as a function of peak wavenumber (wavelength), width, and transmittance. For each of the three signal channels the fitted Gaussians are co-added over 51 pixels where the transmittance is largest for a representative filter function for that channel. The transmittances are not absolutely calibrated in photometric units, but the relative transmittance between channels and between detectors is maintained, which allows for the retrieval of temperature at the tangent altitude.
Estimated bias uncertainties in derived temperatures by altitude; aka systematic uncertainties. These uncertainties are present in each temperature profile and are primarily due to 1) a 1 cm-1 uncertainty in the common shift applied to pre-flight laboratory determined filter positions. This uncertainty was tested in the retrieval and a derived fixed uncertainty of 12 K is propagated at all altitudes and 2) the lack of measurements above the top altitude sampled, and altitude dependent, with the topmost altitudes of the retrieval affected the most. The temperature bias uncertainty is found by a root sum square of these two. At most altitudes the estimated bias uncertainty is dominated by the uncertainty in the common shift.
Statistical uncertainties (one sigma) in derived temperatures by altitude.
Total uncertainties in derived temperatures by altitude: Here the statistical temperature uncertainty has been linearly added to the estimated temperature bias.
Cold-side temperature of the thermoelectric cooler attached to the camera head.
This variable is the same as Epoch but is formatted as a human-readable string.
Milliseconds since 1970-01-01 00:00:00 UTC at start of image integration. Derived from original GPS values reported from spacecraft (Time_GPS_Seconds and Time_GPS_Subseconds). Time calculation is offset by 615ms (flush time) for the first image in the series and for all other images are adjusted by subtracting (integration time + 308 milliseconds) from the reported GPS time.
Milliseconds since 1970-01-01 00:00:00 UTC at end of image integration. Derived from original GPS values reported from spacecraft (Time_GPS_Seconds and Time_GPS_Subseconds). Time calculation is offset by 615ms (flush time) for the first image in the series and for all other images are adjusted by subtracting (integration time + 308 milliseconds) from the reported GPS time.
Aperture Position 1: 0=OPEN, 1=CLOSED, 2=15% OPEN, 3=UNKNOWN. Note that when OPEN (0) the integration time is 60 s for nighttime observations and when 15% OPEN (2) the integration time is 30 s for daytime observations.
Aperture Position 2: 0=OPEN, 1=CLOSED, 2=15% OPEN, 3=UNKNOWN. Note that when OPEN (0) the integration time is 60 s for nighttime observations and when 15% OPEN (2) the integration time is 30 s for daytime observations.
Spacecraft altitude at middle of exposure.
Spacecraft latitude at middle of exposure.
Spacecraft local solar time (0-24) at middle of exposure.
Spacecraft longitude (0-360) at middle of exposure.
Spacecraft solar zenith angle at middle of exposure.
Flag indicating that the spacecraft is ascending (0) or descending (1) node.
Orbit Number