The Ozone Monitoring Instrument (OMI) is an ultravioletvisible imaging spectrograph that uses two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction. This allows having a 114 degrees wide swath combined with an unprecedented small ground pixel (nominally 13 x 24 km2), which in turn enables global daily ground coverage with high spatial resolution. The OMI instrument is part of NASA’s EOSAURA satellite, which will be launched in the second half of 2004. The on-ground calibration of the instrument was performed in 2002. This paper presents and discusses results for a number of selected topics from the on-ground calibration: the radiometric calibration, the spectral calibration and spectral slit function calibration. A new method for accurately calibrating spectral slit functions, based on an echelle grating optical stimulus, is discussed. The in-flight calibration and trend monitoring approach and facilities are discussed.
KEYWORDS: Solar energy, Renewable energy, Data modeling, Atmospheric modeling, Wind energy, Satellites, Solar radiation models, Energy efficiency, Systems modeling, Environmental sensing
Earth observations have played an increasing role in informing decision making in the energy sector. In renewable
energy applications, spaceborne observations now routinely augment sparse ground-based observations for solar energy
resource assessment. As one of the nine Global Earth Observing System of Systems (GEOSS) societal benefit areas, the
enhancement of policy and management decision making in the energy sector is receiving considerable attention in
activities conducted by the Committee on Earth Observation Satellites (CEOS). We describe current projects being
conducted by CEOS member agencies to partner with end-user energy decision makers to enhance their decision support
systems using space-based observations. These prototype projects have frequently been pursued through the Group on
Earth Observations (GEO) Energy Community of Practice and, more recently, in collaboration with the CEOS Energy
societal benefit area (SBA). Several case studies exhibiting the utility of Earth observations to enhance renewable energy
resource assessment, forecast space-weather impacts on the power grid, and optimize energy efficiency in the built
environment are discussed.
The NPOESS Ozone Mapping and Profiler Suite (OMPS) will collect data to permit the retrieval of the vertical and horizontal distribution of ozone in the Earth's atmosphere. Algorithm development efforts in connection with these measurements include the preparation of Algorithm Theoretical Basis Documents (ATBDs), Operational Algorithm Documents (OADs), and science grade code with associated test sets and documentation. These items are provided to the Interface Data Processing Segment (IDPS) for conversion and integration into the operational system. This paper addresses elements of the process being used to convert, test, and maintain the maturing and changing science grade code to the initial operational source code for the OMPS. The operational OMPS SDRs and EDRs will be generated by the IDPS, that is, ozone output items will include the sensor and environmental data records, associated metadata and product validation; e.g. ancillary data, calibration information and quality flags.
The Ozone Mapping Profiler Suite will produce ozone profiles using the limb scatter technique. While this technique has been used in the 1980s for mesospheric retrievals with data from the Solar Mesospheric Explorer, its use for the stratosphere and upper troposphere is relatively recent. To increase the scientific experience with this method, the Limb Ozone Retrieval Experiment LORE was flown on-board STS107 in 2003. A significant amount of data from
thirteen orbits was down-linked during the mission and exists for analysis. LORE was an imaging filter radiometer, consisting of a linear diode array, five interference filters (plus a blank for dark current) and a simple telescope with color correcting optics. The wavelengths for the channels were 322, 350, 602, 675 & 1000 nm and can be viewed as a minimum set of measurements needed for ozone profiling from 50 km to 10 km. The temporal sampling of the channels, along with the shuttle orbital and attitude (e.g. pitch) motions present a challenge in retrieving precise ozone profiles. Presented are the retrieval algorithms for determination of the channel's altitude scale, cloud top height and aerosol extinction. Also shown are a sub-set of flight data and the corresponding retrieved ozone profiles.
One retrieval technique of ozone profiles using scattered light from the limb of the atmosphere utilizes measurements made high in the atmosphere as a reference. While this procedure relaxes the radiometric accuracy required, it accentuates the need for stray light characterization. In addition, when the entire limb (all altitudes of interest) is imaged simultaneously, as done by the Limb Ozone Retrieval Experiment (LORE) with a linear diode array, the stray light must be characterized for the reference altitude to within 1.0e-04 of the maximum signal in the field of regard (typically at the lowest altitudes). For this system this further translates into the need to know the spatial point-spread function over 5-6 orders of magnitude. We demonstrate the use of pre-flight laboratory instrument characterization, in flight observations and radiative transfer modeling to characterize the stray light of LORE during STS107.
The Ozone Monitoring Instrument is an UV-Visible imaging spectrograph using two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction. This allows having a wide swath (114 degrees) combined with a small ground pixel (nominally 13 x 24 km2). The instrument is planned for launch on NASA’s EOS-AURA satellite in January 2004. The on-ground calibration measurement campaign of the instrument was performed May-October 2002, data is still being analyzed to produce the calibration key data set. The paper highlights selected topics from the calibration campaign, the radiometric calibration, spectral calibration including a new method to accurately calibrate the spectral slitfunction and results from the zenith sky measurements and gas cell measurements that were performed with the instrument.
Ozone Monitoring Instrument (OMI) is a Dutch-Finnish ozone monitoring imaging spectrometer that is designed to provide accurate measurements of total column ozone, ozone profile, surface UV irradiance, aerosols and cloud characteristics, and the column amounts of trace gases SO2, NO2, HCHO, BrO, and OClO at high spatial resolution. The OMI along with the three other instruments, the Microwave Limb Sounder (MLS), the High Resolution Dynamics Limb Sounder (HIRDLS), and the Tropospheric Emission Spectrometer (TES), will be flown on the NASA’s Aura mission in early 2004. The standard atmospheric chemistry and dynamics products derived from OMI, MLS, and HIRDLS will be archived at the NASA's GES DAAC (TES data products will be archived at NASA Langley Research Center DAAC) and will be freely available to the public. Highlights of OMI data products, as well as their availability, distribution and data support are discussed in this paper.
The Ozone Monitoring Instrument (OMI) is an UV-Visible imaging spectrograph using two dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction. This allows having a wide swath (114 degrees) combined with a small ground pixel (nominally 13 x 24 km). The instrument is planned for launch on NASA's EOS-AURA satellite in June 2003. Currently the OMI Flight Model is being build. This shortly follows the Instrument Development Model (DM) which was built to, next to engineering purposes, verify the instrument performance. The paper presents measured results from this DM for optical parameters such as distortion, optical efficiency, stray light and polarization sensitivity. Distortion in the spatial direction is shown to be on sub-pixel level and the stray light levels are very low and almost free from ghost peaks. The polarization sensitivity is presently demonstrated to be below 10-3 but we aim to lower the detection limit by an order of magnitude to make sure that spectral residuals do not mix with trace gas absorption spectra. Critical detector parameters are presented such as the very high UV quantum efficiency (60 % at 270 nm), dark current behavior and the sensitivity to radiation.
The Ozone Monitoring Instrument (OMI) is a UV/VISible spectrograph (270 - 500 nm). It employs two-dimensional arrays of CCD detectors for simultaneous registration of numerous spectra from ground pixels in the swath perpendicular to the flight direction. As a result, OMI provides (almost) daily global coverage in combination with small ground pixel sizes (nominally 13 X 24 km2 at nadir, minimum 13 X 12 km2 at nadir). The small ground pixels allow retrieval of tropospheric constituents. The OMI Flight Model is currently being integrated and will be launched on the Aura satellite in2003 as part of NASA's Earth Observing System. This paper discusses relationships between and the details of the on-ground calibration approach of OMI, the data processing of level 0 data (raw data) to level 1b data (geophysical data) and the foreseen activities for in-flight calibration.
The Ozone Monitoring Instrument (OMI) is a UV/VIS spectrograph (270-500 nm) in the line of GOME3 and SCIAMACHY4. It employs two-dimensional CCD detectors for simultaneous registration of numerous spectra from ground pixels in the swath perpendicular to the flight direction. The OMI field of view is 13 x 2600 km2 per two seconds nominal exposure time providing (almost) daily global coverage in combination with small ground pixel sizes (nominally 13 x 24 km2, minimum 13 x 12 km2). The small ground pixels will allow retrieval of tropospheric constituents. The OMI contains various new and innovative design elements such as a polarisation scrambler and programmable CCD read-out modes. This paper discusses the overall design of the OMI together with the instrumental capabilities.
The Ozone Monitoring Instrument (OMI) is a Dutch-Finnish contribution to NASA's EOS-Chemistry satellite, which is due to be launched in December 2002. The aim of OMI is to contribute to climate monitoring and atmospheric chemistry research by providing daily global measurements of the total ozone column, ozone profile, NO2 column, other trace gases like SO2 and BrO2, aerosols, cloud fraction, cloud to pressure, and surface UV irradiance.
All but one of the backscatter UV (BUV) instruments have used solar reflective diffusers made of ground aluminum to maintain instrument calibration after launch. These diffusers have been sued throughout mission life-times, which range from less than 1 years to over 14 years. Means for monitoring diffuser reflectance include mechanisms on the instruments as well as methods to infer reflectance using earth radiance data. We compare changes in diffuser reflectance for the various instruments and find some common behavior as well as significant differences. Changes which appear to occur at different rates are actually quite similar when corrections are made for the amount and direction of incident solar irradiation. However, a class of instruments, the SBUV/2, has significantly lower degradation rates. We find, as have previous authors, that spacecraft self-contamination is the most likely cause of diffuser changes and observed differences. Observed changes suggest that contaminant layer thickness is the main reflectance degradation mechanism in the first few years of operation.
KEYWORDS: Transmittance, Optical filters, Interference filters, Humidity, Temperature metrology, Linear filtering, Signal to noise ratio, Ionizing radiation, Sensors, Ultraviolet radiation
A series of in-band and out-of-band transmittance measurements of filters covering the wavelength range from 317 to 1019 nm and a linear variable filter for the 300 to 400 nm range have been made. The bandpass filters and the linear variable were fabricated using the ion-assisted-deposition or similar processes. The radiometric stability of the central wavelength, bandpass (FWHM), and peak transmittances were measured before and after exposures to combined high temperature and humidity, a thermal vacuum cycle, an ionizing particle radiation environment, flight on the Space Shuttle and at two temperature ranges. Representative radiative signal-to-noise ratios are given for solar irradiance observations with a silicon photodiode detector.
New developments in interference filter technology utilizing low thermal expansion coefficient materials which are deposited free of voids using variants of ion-assisted- deposition techniques have made possible the development of a new class of low-cost, lightweight remote sensing instruments. These instruments can easily have a throughput two orders of magnitude larger than similar dispersive monochromators in addition to having a stray light rejection somewhere between that of a single and a double monochromator for a bandpass of the order of one nanometer. Results from environmental testing, measurements of stability in space, and unique problems associated with spectral radiance calibrations with these interference filter instruments are described.
The improved TOMS instruments, flight models 3, 4, and 5, are to be flown aboard Earth probe (EP), Japanese ADEOS, and Russian Meteor-3M satellites, respectively. TOMS obtains the total column amount of the atmospheric ozone from measurements of the extra-terrestrial solar spectral irradiance and the backscattered earth spectral radiance at six ultraviolet wavelengths between 308.6 nm and 360 nm. The added scientific goal of new generation instruments is to monitor the trend of the global burden of the atmospheric ozone, which requires an accuracy of 1% in the calibration for the ratio of the radiance to the irradiance measurements. The emphasis of the prelaunch-calibration approaches was to maximize the accuracy in the ratio of the calibration for the two measurement modes and to minimize possibility of the systematic errors. The source geometry was maintained as close as possible in the calibration setup for the two measurement modes so that the uncertainty associated with the source could be canceled out in the ratio of the two calibrations. Also, multiple calibration techniques and radiometric sources have been used to check consistency of the calibration. The FM-3 calibration results show a three sigma standard errors of the mean for the ratio calibration that range from 0.28% to 0.63% in descending order of the wavelength.
We discuss several new uses of backscatter ultraviolet (UV) measurements in atmospheric remote sensing. Radiances in the UV from 310 - 340 nm are primarily sensitive to total ozone and the effects of clouds and the Earth's surface. We have modeled UV radiances in this spectral range to an accuracy of approximately 0.5% with an efficient radiative transfer model. We have retrieved accurate values of total ozone using continuous spectral scan mode data from the Nimbus 7 Satellite Backscatter Ultraviolet (SBUV) spectrometer. Systematic effects resulting from calibration and algorithmic errors have been removed. The continuous scan mode total ozone measurements serve as independent validation of total ozone measurements and trends derived from TOMS and SBUV discrete mode, both of which have better temporal and spatial coverage than SBUV continuous scan mode but fewer channels. At wavelengths between 340 and 400 nm, radiances are sensitive to several properties of clouds and aerosols. We have used rotational-Raman scattering signatures near 360 nm and at the 394 nm calcium solar Fraunhofer line to determine effective UV cloud pressures with both TOMS and SBUV in continuous scan mode. At 280 nm, resonance scattering from magnesium ions has been detected. Spatial and temporal variations in magnesium ion column abundances, including increases with increased solar activity, have been derived from SBUV continuous scan measurements.
A new instrument has been developed to measure spacecraft attitude which utilizes ultraviolet radiation scattered in the Earth's limb. The sensor consists of a very stable UV bandpass filter with a center wavelength at 355 nm, imaging optics, and a linear diode array detector. The radiance of the limb at this wavelength is dominated by Rayleigh scattering and typically decreases by 15% per kilometer above 20 km. The theoretical resolution at the limb of this device is 0.39 km per pixel for a nominal orbital altitude of 306 km (approximately equals 0.012 degree(s)) and represents a significant improvement over typical infrared-based attitude sensors which have an accuracy of approximately equals 0.1 degree(s). This system was integrated with the Shuttle Solar Backscatter Ultraviolet experiment and flown on STS-72 in January of 1996. The calibration and optical characterization of the device will be presented. Results from the first flight of this instrument, showing an agreement with available shuttle pointing data of +/- 0.05 degree(s), will also be discussed.
Beginning in the mid 1960's large aperture scanning radiometers have been used in space to determine spectroradiometric properties of earth scenes in the red and near infrared regions. Panel diffusers as calibration sources for these radiometers were abandoned in favor of internally illuminated integrating spheres because of problems of illuminating the panel diffuser uniformly.1 Since 1970 spectroradiometric instruments used in space for remote sensing of the atmosphere in the ultraviolet for the determination of stratospheric ozone and total column amounts have used spectral radiance calibrations derived from calibrated panel diffusers illuminated by NIST standards of spectral irradiance. An advantage of the panel diffuser technique is simplicity of the experimental set up. Stratospheric ozone profiles and total column amounts are derived from ratios of atmospheric radiances to corresponding solar irradiances incident at the top of the atmosphere in the wavelength region of 250 - 340 nm. An inherent problem associated with measurements for the remote sensing of stratospheric ozone which is not shared with remote sensing measurements of earth scenes at longer wavelengths of the solar scattering and reflective region is the extremely large dynamic range of atmospheric radiances and the steep gradients of radiance with wavelength. For a typical wavelength scan the spectral radiance changes by about lO and the average signal level of a spectral scan can shift by another factor of 25 or more due to solar zenith angle changes between the subsolar point and the solar zenith angle limit of useful scan information which is within a couple of degrees of the terminator. The derivation of spectral radiance calibrations using either the sphere or panel diffuser techniques for ultraviolet remote sensing instruments are single point calibrations at each wavelength. A subsequent linearity calibration of the detector and electronics is made in non dispersed or white light over the entire dynamic range of the instrument of more than six decades. Consequently the derived radiometric calibration constants consist of a radiometric sensitivity term and a signal dependent linearity correction. An initial comparison of spectral radiance calibrations of SBUV-2 instruments using spherical integrator and panel diffuser techniques has been given by Heath et al.2. Subsequent work by Heath et al. describes the results from comparisons of four spectral radiance calibrations derived using panel diffuser techniques with five spectral radiance calibrations derived using spherical integrator techniques for three different SBUV-2 instruments. The comparability of the sphere and panel diffuser spectral radiance calibration techniques is assesed by comparing derived average BRDF values of panel diffusers based upon the sphere technique with laboratory measurements of BRDF of the panel diffusers. The sphere radiances determined relative to NIST standards of spectral irradiance are compared with measurements of sphere radiance relative to a NIST high temperature blackbody source. This work describes the evaluation of the consistency of spectral radiance calibration scales established using panel diffuser and internally illuminated spherical integrator techniques for the SSBUV and SBUV-2 Flight Model 5 instruments using zenith sky radiance measurements as a function of solar zenith angle (UMKEHR) which coincident in space and time. Also described are the spectral radiance calibrations of the Global Ozone Monitoring Experiment (GOME) with the NASA sphere which has been used to intercalibrate SBUV-2 and SSBUV instruments. These spectral radiance calibration constants are compared with those derived using a Spectralon panel diffuser whose BRDF was measured at NASA Goddard Space Flight Center by J. Butler.
Many remote sensing instruments employ diffuse targets for calibration. These targets usually consist of diftusers with high Lambertian characteristics illuminated by a calibrated irradiance source. There is increasing interest in conducting in-orbit radiance calibration checks of remote sensing instruments using sunlight reflected off a diffuser. We report on the effects of space flight on the reflectance properties of polytetrafluoroethylene (PTFE) and aluminum diffuser samples flown on three Space Shuttle flights. These experiments showed good stability of both diffuser types in the visible and near infrared but experienced measurable degradation in the ultraviolet. Degradation varied from flight to flight and seemed to be related to different levels of contamination experienced on the three flights.
Spectral radiance calibrations have been made for several SBUV/2 instruments using techniques based upon an internally illuminated spherical integrator and diffuse reflectance panels with BRDF measurements from NIST. Both techniques are referenced to NIST standards of spectral irradiance which are used to derive the spectral irradiance calibrations of the instruments. The spectral radiance of the aperture of the internally illuminated spherical integrator also has been calibrated by NIST against a high temperature blackbody. The consistency of the spectral radiance calibrations and the problems specific to each of the techniques are described.
A comparison has been made of spectral radiance calibrations of SBUV-2 instruments using two techniques. In one, a source of spectral radiance is obtained by illuminating a spectralon panel diffuser whose BRDF has been measured by NIST with a 1000 W FEL quartz-tungsten- halogen standard of spectral irradiance from NIST. In the other, the spectral irradiance of the aperture of an internally illuminated spherical integrator is measured relative the same NIST standard of spectral irradiance used with the panel diffuser. The spectral radiance of the sphere is calculated for a source of irradiance which is uniform and radiates as a Lambertian source over the area of the aperture. The agreement between the average of four spectral radiance calibrations of SBUV-2 instruments obtained with the spectralon panel diffuser technique with those obtained from five spectral radiance calibrations with the internally illuminated spherical integrator technique is better than one percent in the wavelength range of 250 - 340 nm. Repeated use of two spectralon panel diffusers over a two year period indicates a stability of diffuser BRDF of better than one percent.
In this study we report on the effects of space flight on the reflectance properties of PTFE (polytetrafluorethylene) and aluminum diffuser samples that were flown along with the Shuttle Solar Backscatter Ultraviolet experiment on STS-43, STS-45, and STS-56. These initial experiments showed good stability in the visible and near infrared with some degradation in the ultraviolet which vary from flight to flight which could be attributed to different amounts of contamination levels. This paper reports on the diffuser material processing, the space environment experienced, and the results of the reflectance measurements and the surface chemical analysis before and after flight.
The Shuttle Solar Backscatter Ultraviolet (SSBUV) spectrometer instrument provides regular in-orbit calibration checks on the SBUV/2 ozone/solar irradiance monitoring instruments which are being flown routinely on NOAA operational satellites. The goal of the long-term ozone monitoring program is to detect possible changes in stratospheic ozone with a two sigma accuracy of approximately 1 percent over the course of a decade. This translates into a requirement that the SSBUV instrument be calibrated to a one sigma precision of 1 percent at the wavelengths used for ozone monitoring. We have previously shown that the precision of the SSBUV calibrations is such that we can meet this requirement. Here we discuss SSBUV radiometric sensitivity changes occurring as a result of the first two Space Shuttle flights. Finally, we present and compare SSBUV solar irradiance measurements taken during these flights.
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