Monitoring aerosols in the stratosphere requires measurements with good vertical resolution and comprehensive spatial sampling. We have developed a small satellite instrument that utilizes the limb scattering observation technique to meet these requirements. The Aerosol Radiometer for Global Observation of the Stratosphere (ARGOS) instrument measures radiance profiles in eight equally spaced directions simultaneously, using two near-infrared wavelengths (870nm and 1550nm) to improve penetration into the upper troposphere and lower stratosphere (UT/LS). The combination of multiple viewing directions and multiple wavelengths provides improved spatial sampling and statistical leverage to validate the particle size distribution used to retrieve aerosol extinction. ARGOS is scheduled for a technology demonstration flight in February 2025.
Adverse air quality impacts human health and climate and has implications for environmental equity. The Compact Hyperspectral Air Pollution Sensor (CHAPS) is a newly designed small imaging spectrometer for remote sensing of nitrogen dioxide (NO2) and other air pollutants from space. It incorporates two emerging technologies, to achieve the miniaturization necessary to fit within a 6U CubeSat. The first is freeform optics, which can be used to reduce the size of an imaging spectrometer without compromising optical performance. We report the science requirements; preliminary, fully freeform and fully reflective optical design of the CHAPS demonstrator, CHAPS-D; and model its performance. The second technology is additive manufacturing, coupled with topology optimization, which has a number of potential advantages over traditional subtractive manufacturing. The instrument mechanical structure, including optical mounts and integral light baffles, and two of the optical elements will be additively manufactured using a high-strength nextgeneration aluminum alloy. We show preliminary results of additive manufacturing tests. CHAPS-D is currently being developed for ground-based and airborne testing.
Next generation air quality sensors are currently planned to launch in the 2020-2021 timeframe. The Tropospheric Emissions: Monitoring of Pollution (TEMPO-United States) and Geostationary Environment Monitoring Sensor (GEMSKorea) are two such missions that will probe the boundary layer and lower troposphere at unprecedented spatial and temporal scales. These missions are designed to provide constraints on chemical forecast models and specifically to answer the question: “What are the temporal and spatial variations of emissions of gases and aerosols important for air quality and climate?” In preparation for these missions a number of airborne air quality field missions have been performed to collect data at similar spatial and temporal scales, and during relevant seasonal air quality episodes. This data is being used to improve the trace gas retrieval algorithms and explore the unique spatial scales and diurnal patterns that will be encountered when the Geostationary experiments are operational. This overview will present details of two of the instruments used during these campaigns, the GEO-CAPE Airborne Simulator (GCAS) and the Geostationary Trace Gas and Aerosol Sensor Optimization (GeoTASO) instruments. The instruments' performance will be compared to predicted on-orbit values for the TEMPO and GEMS sensors in the retrieval of high spatial resolution nitrogen dioxide and formaldehyde. Examples of vertical column retrievals will be presented under various source/weather conditions as well as some of the uncertainties that result from radiative transfer assumptions.
The GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) was developed at NASA’s Goddard Space Flight Center (GSFC) and has flown in multiple field campaigns to perform mapping of the regional-scale EPA criteria pollutants nitrogen dioxide, ozone, and formaldehyde. GCAS will also participate in validation campaigns for NASA’s Tropospheric Emissions: Monitoring POllution (TEMPO) mission and the Korean Geostationary Environment Monitoring Spectrometer (GEMS) mission, both scheduled to launch in the early 2020s. GCAS houses two commercial Offner-type grating spectrometers that measure backscattered solar spectral radiance from the near-ultraviolet to near-infrared at high spatial resolution (typically 250 meters at 8.5 kilometer altitude). These radiances are used to retrieve spatial and temporal distributions of trace gases relevant to the boundary layer and free tropospheric atmospheric chemistry cycles. In this paper, we describe the field calibration techniques employed to characterize the spectral and temporal radiometric stability of the system during its most recent deployment in the 2018 Long Island Sound Trace Ozone Study (LISTOS) field campaign. Overall measurement uncertainty, retrieval impacts, and lessons learned for future deployments will also be described.
The NASA ESTO-funded Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) development project demonstrates a reconfigurable multi-order airborne spectrometer and tests the performance of spectra separation and filtering on the sensor spectral measurements and subsequent trace gas and aerosol retrievals. The activities support mission risk reduction for the UV-Visible air quality measurements from geostationary orbit for the TEMPO and GEMS missions1 . The project helps advance the retrieval algorithm readiness through retrieval performance tests using scene data taken with varying sensor parameters. We report initial results of the project.
The Geostationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) was designed and built at the NASA Goddard Space Flight Center (GSFC) as a technology demonstration instrument for the atmospheric science study group of GEO-CAPE and potential validation instrument for NASA’s Tropospheric Emissions: Monitoring Pollution (TEMPO) mission. GCAS was designed to make high altitude remote sensing observations of tropospheric and boundary layer pollutants, coastal and ocean water leaving radiances, and visible imagery for cloud and surface information. The instrument has participated in one flight campaign in Houston, TX as part of the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) in September 2013. An overview of the instrument’s design, characterization, and preliminary slant column retrievals of nitrogen dioxide (NO2) and ozone (O3) during the DISCOVER-AQ campaign will be provided in this paper.
OMPS is the latest advanced hyperspectral sensor suite flying onboard the Suomi National Polar-Orbiting Partnership
(Suomi NPP) spacecraft. It measures ozone depletion in total column and vertical profile ozone abundances. OMPS on-orbit
calibration is conducted through dark, lamp and solar measurements. Launched on October 28, 2011, OMPS Nadir
has successfully undergone a thorough early orbit check (EOC) and is currently in the intensive calibration and
validation (ICV) phase. The calibration data gathered during the on-orbit calibration and validation activities allows us to
evaluate the sensor’s early orbit performance and establish on-orbit calibration baseline. In this paper, we provide details
of the sensor major on-orbit calibrations activities and present sensor level performance and calibration results from
OMPS early orbit image data. These results have demonstrated that the OMPS has made a smooth transition from
ground to orbit, and its early on-orbit performance meets or exceeds sensor level requirements and agrees with the
predicted values determined during the prelaunch calibration and characterization. Examples of Nadir CCD orbital
performance monitoring are provided.
The Ozone Mapping Profiler Suite (OMPS) was launched aboard the Suomi National Polar-orbiting Partnership (Suomi
NPP) spacecraft on October 28, 2011. OMPS is meant to continue NOAA/NASA's long-term ozone data record and
bridge the gap to the Joint Polar Satellite System (JPSS) missions later this decade. We present results from the OMPS
Nadir and Limb sensors' early orbit checkout (EOC) operations with comparisons to pre-launch thermal vacuum tests.
Characterization measurements of detector performance show that offset, gain, and read noise trends remain within 0.2%
of the pre-launch values with significant margin below sensor requirements. Nadir Total Column detector dark
generation rate trends show a slow growth in both halves of the focal plane as compared to initial on-orbit
measurements.
Nadir solar calibration measurements remain within 2% of the initial in-flight observation and indicate no spatially
dependent change to within 1%. Limb Profiler solar calibration trending indicate a potential goniometry correction error
as high as 5%. Spectral registration changes based on solar observations are determined to be less than one pixel for the
Nadir Total Column and Limb sensors but approximately one pixel for Nadir Profiler. Preliminary comparisons to
Thullier reference solar spectral irradiances show wavelength dependent differences greater than 5%.
The NASA Goddard Space Flight Center (GSFC) Radiometric Calibration Laboratory (RCL) maintains several large integrating sphere sources covering the visible to the shortwave infrared wavelength range. Two critical, functional requirements of an integrating sphere source are short- and long-term operational stability and repeatability. Monitoring the source is essential in determining the origin of systemic errors, thus increasing confidence in source performance and quantifying repeatability. If monitor data falls outside the established parameters, this could be an indication that the source requires maintenance or recalibration against the National Institute of Science and Technology irradiance standard. The GSFC RCL has developed a Filter Radiometer Monitoring System (FRMS) to continuously monitor the performance of its integrating sphere calibration sources in the 400 to 2400 nm region. Sphere output change mechanisms include lamp aging, coating (e.g., BaSO4) deterioration, and ambient water vapor level. The FRMS wavelength bands are selected to quantify changes caused by these mechanisms. The FRMS design and operation are presented, as well as data from monitoring four of the RCL's integrating sphere sources.
Optical spectroradiometers used to measure and monitor the radiance output of uniform sources must be thoroughly
characterized. The viability of the use of an instrument for such purposes is based upon the establishment of knowledge
of its radiometric responsivity characteristics. The NASA Goddard Space Flight Center Radiometric Calibration
Laboratory (RCL) has commissioned a new spectroradiometer for use in measurements of irradiance and radiance
sources. The spectroradiometer is comprised of a commercial scanning grating, Czerny-Turner double monochromator.
This spectroradiometer has been used to make measurements on a number of irradiance and radiance sources over the
wavelength range of 300 to 2400 nm. Instrument characterization included determination of stability, functional
wavelength calibration and scattered light performance. Comparison measurements were also made with other
radiometers. The data gathered from these measurements is presented, analyzed, and discussed.
The Airborne Compact Atmospheric Mapper (ACAM) was designed and built at the NASA Goddard Space Flight
Center (GSFC) as part of an effort to provide cost-effective remote sensing observations of tropospheric and boundary
layer pollutants and visible imagery for cloud and surface information. ACAM has participated in three campaigns to
date aboard NASA's Earth Science Project Office (ESPO) WB-57 aircraft. This paper provides an overview of the
instrument design and summarizes its ability to determine the minimal measurable slant-column concentration of
nitrogen dioxide (NO2) as well as exploring the calibration stability of commercially available miniature spectrometers.
The NASA Goddard Space Flight Center (GSFC) Radiation Calibration Facility (RCF) maintains several large
integrating sphere sources covering the visible and near infrared wavelength range. Two critical requirements of an
integrating sphere source are short and long-term operational stability and repeatability. Monitoring the source is
essential in determining the origin of systemic errors, thus increasing confidence in source performance, and quantifying
repeatability. If monitor data falls outside the established parameters, this is an indication that the source requires
maintenance or re-calibration against the National Institute of Science and Technology (NIST) irradiance standard. The
GSFC RCF has developed a Filter Radiometer Monitoring System (FRMS) to continuously monitor the performance of
its integrating sphere calibration sources in the 400-2400nm region. Sphere output change mechanisms include lamp
aging, coating (BaSO4) deterioration, and ambient water vapor level. The FRMS wavelength bands are selected to
quantify changes caused by these mechanisms. The FRMS design and operation is presented, as well as data from
monitoring three of the RCF's integrating sphere sources.
In June 2007, a spherical integrating source was calibrated in the National Aeronautics and Space Administration
(NASA) Goddard Space Flight Center's (GSFC) Calibration Facility as part of the prelaunch characterization program
for the NPOESS Preparatory Program (NPP) Ozone Mapping and Profiler Suite (OMPS) instrument. Before shipment to
the instrument vendor, the sphere radiance was measured at the Remote Sensing Laboratory at the National Institute of
Standards (NIST) and then returned to the NASA Goddard facility for a second calibration. For the NASA GSFC calibration,
the reference was a set of quartz halogen lamps procured from NIST. For the measurement in the Remote
Sensing Laboratory, the reference was an integrating sphere that was directly calibrated at NIST's Facility for Spectroradiometric
Calibrations (FASCAL). For radiances in the visible and near-infrared (400 nm to 1000 nm), the agreement
between the NASA GSFC calibration and the validation measurements at the Remote Sensing Laboratory was at the 1 %
level. For radiances in the near ultraviolet (250 nm to 400 nm), the agreement was at the 3 % level.
In-flight performance and calibration results of the Ozone Monitoring Instrument OMI, successfully launched on 15 July
2004 on the EOS-AURA satellite, are presented and discussed. The radiometric calibration in comparison to the high-resolution
solar irradiance spectrum from the literature convolved with the measured spectral slit function is presented. A
correction algorithm for spectral shifts originating from inhomogeneous ground scenes (e.g. clouds) is discussed.
Radiometric features originating from the on-board reflection diffusers are discussed, as well as the accuracy of the
calibration of the instrument's viewing properties. It is shown that the in-flight performance of both CCD detectors shows
evidence of particle hits by trapped high-energetic protons, which results in increased dark currents and increase in the
Random Telegraph Signal (RTS) behaviour.
The Ozone Monitoring Instrument (OMI) was launched on 15 July 2004 on NASA's EOS AURA satellite. The OMI instrument is an ultraviolet-visible imaging spectrograph that uses two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction with a 115 degrees wide swath, which enables global daily ground coverage with high spatial resolution. This paper presents a number of in-flight radiometric and spectral instrument performance and calibration results.
Launched on 15 July 2004 aboard the EOS AURA satellite, the Ozone Monitoring Instrument (OMI) is intended as the successor to the Total Ozone Mapping Spectrometer (TOMS). OMI's improved horizontal spatial resolution and extended wavelength range (264-504nm) will provide total column ozone, surface reflectance, aerosol index, and ultraviolet (UV) surface flux as well as ozone profiles and tropospheric column ozone, trace gases, and cloud fraction and height. We present results from a variety of calibration techniques that have been developed over the years to assess the calibration accuracy of backscatter UV sensors. Among these are comparisons of OMI solar measurements with external solar reference spectra and radiances measured over Antarctica and Greenland. OMI UV measured irradiances show wavelength dependencies and spectral features on order of 5% when compared to external solar spectra while all channels exhibit a nearly wavelength independent 1% seasonal goniometric error. No instrument throughput degradation has been identified beyond this level and has been confirmed through ice radiance comparisons. A 3% OMI radiance cross-track swath dependence is seen when comparing radiances over ice fields to radiative transfer results. Reflectances derived at low latitudes show the same cross-track swath dependence with an additional 5% offset.
The Optical Radiation Measurement (ORM) group of the National Physical Laboratory is responsible for the development of the UK's primary radiometric quantities. One of its principle aims in recent years has been to improve the accuracy of "user" measurements through improved traceability routes to the SI system of units. The Earth Observation (EO) community is arguably the most demanding, requiring specialist techniques and transfer standards.
To improve accuracy, NPL has developed a range of lamp illuminated integrating spheres, called Transfer Standard Absolute Radiance Source (TSARS). The TSARS is calibrated directly against the NPL primary blackbody source with uncertainties <±0.75% which can be maintained and confirmed following transportation, through detector stabilisation. To demonstrate the performance of NPL's new TSARS, it was taken to TNO TPD in Delft for inclusion in the radiometric characterisation of the Global Ozone Monitoring Experiment (GOME 2) - FM3.
Overall agreement to <± 1% with both TNO TPD and NASA was achieved, demonstrating consistency in international radiometric scales, since the TNO and NASA sources were calibrated traceable to NIST. It also demonstrates the practicality of achieving calibrations with uncertainties <±1%, and since the NPL TSARS is portable, allows similar levels of uncertainty in "field situations" e.g. field spectrometers, aircraft radiometers.
The polarization sensitivity of a Brewer MKIII double spectrophotometer was measured in the laboratory. We found two major sources of polarization sensitivity. 1) The flat quartz plate as the first optical element alters the polarization state of the transmitted light by Fresnel reflection at oblique incident angles. 2) The internal grating produces almost 100% polarization of the incident light perpendicular to the direction of the ruled grating. The combination of both effects results in a zenith angle (ZA) dependence of the instrument’s sensitivity for unpolarized input such as from Direct Sun measurements. The Brewer is 2% more sensitive at ZA=0° and 10% less sensitive at ZA=80° with respect to normal incidence (ZA=35°). Since the ZA-dependence is independent of wavelength this effect cancels out when calculating wavelength-ratios as used for total ozone retrieval. However the ZA-dependence causes errors when absolute signals at single wavelengths are needed as for aerosol optical depth (AOD) retrievals. Based on our laboratory measurements an overestimation of the Langley extrapolation between 3% and 5% is estimated even at best atmospheric conditions. The ZA-dependence causes 0.025-0.045 overestimation of AOD and an underestimation of the Angstrom exponent. We believe that this effect has not been detected from Brewer AOD-measurements since it is masked by larger uncertainty sources of other nature and AOD-comparisons to other instruments in the short UV-region are rare. Knowing the ZA-dependence it is possible to correct for the ZA-effect. We modified our Brewer by incorporating a depolarizer in its optical path and replacing the flat quartz window by a curved one, so that the input is always at normal incidence, which reduces the ZA-effect.
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.
A Brewer MKIII double spectrophotometer has been modified to measure direct sun and sky radiance from 303nm to 363nm for the purpose of measuring aerosol optical depth, Angstrom parameter, and single scattering albedo. Results from a detailed instrument calibration showed that there is a temperature dependence of -0.3% per degree Celsius, the field of view was 2.6° full width half maximum, and the wavelength calibration was accurately determined using a dye-LASER. Using both integrating sphere and lamp-diffuser plate combinations, absolute diffuse radiometric calibration was performed and converted into direct calibration using the measured field of view. Aerosol optical depth and Angstrom parameter were measured on 4 clear sky days in June 2003 at Greenbelt, Maryland and compared to AERONET-data at the same location. The average difference in the aerosol optical depth at 340nm was smaller than 0.02. A depolarizing element was inserted in the Brewer's optical path to reduce the very pronounced polarization sensitivity, and additional polarized filters were added to explore the possibility to obtain additional aerosol information. Because of a defect in the depolarizer, the current residual polarization is 5%, which has to be reduced to less than 1% to derive additional aerosol parameters from sky radiance measurements.
12 The Total Ozone Mapping Spectrometer - Flight Model 5 (TOMS- 5), aboard the QuikTOMS spacecraft, is designed to continue the measurement of the total column amount of ozone in the atmosphere in order to monitor the global trend. Since the predicted total ozone change due to man-made sources is very small, an accurate calibration of the measuring instrument is required. Since in the TOMS-5 experiment the total ozone amount is determined from the ratio of the measurement of the solar backscattered ultraviolet Earth radiance to the incident solar irradiance, the accuracy of the calibration of the instrument sensitivity to this ratio measurement is critical. The prelaunch calibration of TOMS-5 was designed to achieve a ratio calibration accuracy of 1% in addition to the uncertainties of the standards used. Multiple calibration techniques were employed to ensure the self- consistency of results of different techniques to eliminate any systematic errors. TOMS-5 prelaunch radiometric calibration was performed twice, one in 1996 and the second in 1999 due to the launch delay. The ratio calibration was reproduced within 0.5% from the tests of 1996 to those of 1999 while the calibration of the individual measurement modes agreed among the various techniques to within 1%.
The Total Ozone Mapping Spectrometer (TOMS) provides daily global mapping of the total column ozone in the earth’s atmosphere. It does this by measuring the solar irradiance and the backscattered solar radiance in 6 spectral bands falling within the range from 308.6 nm to 360 nm. The accuracy of the ozone retrieval is highly dependent on the knowledge of the transfer characteristics and center wavelength for each spectral band. A 0.1 nm wavelength error translates to a 1.6% error in ozone. Several techniques have historically been used to perform the wavelength calibration of the TOMS instruments. These methods include the use of film and reference spectra from low-pressure spectral line lamps and the use of continuum sources with a narrow-band scanning monochromator. The spectral transfer characteristic of the Flight Model 5 instrument for the QuikTOMS mission was calibrated using a new technique employing a frequency doubled tunable dye laser. The tunable laser has several advantages that include a very narrow spectral bandwidth; accurate wavelength determination using a wavemeter; and the ability to calibrate the instrument system level of assembly (prior methods required that the calibration be performed at the monochromator sub assembly level). The technique uses the output from a diode-pumped solid state Nd:V04 laser that is frequency doubled to provide a continuous wave 532 nm pump laser beam to a Coherent Model 899-01 frequency doubled ring dye laser. The output is directed into the entrance port of a 6-inch diameter Spectralon integrating sphere. A GaP photodiode is used to monitor the sphere wall radiance while a Burleigh Wavemeter (WA-1500) is used to monitor the wavelength of the visible output of the dye laser. The TOMS field of view is oriented to view the exit port of the integrating sphere. During the measurement process the response of the instrument is monitored as the laser source is stepped in 0.02-nm increments over each of the six TOMS spectral bands. Results of the new technique allow establishing the wavelength center to a precision of better than 0.1 nm. In addition to the spectral band measurements, the laser provided a means to calibrate the radiometric linearity of the QuikTOMS instrument and yield new insights into the stray light performance of the complete optical system.
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