Scott J. Janz

The retrieval of O3 profiles from limb scatter measurements:Results from the Shuttle Ozone Limb Sounding Experiment

Two instruments were flown on Shuttle flight STS-87 to test a new technique for inferring the ozone vertical profile using measurements of scattered sunlight from the Earths limb. The instruments were an ultraviolet imaging spectrometer designed to measure ozone between 30 and 50 km, and a multi-filter imaging photometer that uses 600 nm radiances to measure ozone between 15 km and 35 km. Two orbits of limb data were obtained on December 2, 1997. For the scans analyzed, the ozone profile was measured from 15 km to 45 km with approximately 3 km vertical resolution. Comparisons with a profile from an ozonesonde launched from Ascension Island showed agreement mostly within ±5%. The tropopause at 15 km appears to have been detected in this comparison. A comparison with two HALOE ozone profiles showed that on average ozone measured by SOLSE was lower by 9%±5% in the 30 km to 45 km range.

Tropospheric emissions: monitoring of pollution (TEMPO)

TEMPO was selected in 2012 by NASA as the first Earth Venture Instrument, for launch circa 2018. It will measure atmospheric pollution for greater North America from space using ultraviolet and visible spectroscopy. TEMPO measures from Mexico City to the Canadian tar sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution (~2 km N/S×4.5 km E/W at 36.5°N, 100°W). TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry. Measurements are from geostationary (GEO) orbit, to capture the inherent high variability in the diurnal cycle of emissions and chemistry. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies. TEMPO takes advantage of a commercial GEO host spacecraft to provide a modest cost mission that measures the spectra required to retrieve O3, NO2, SO2, H2CO, C2H2O2, H2O, aerosols, cloud parameters, and UVB radiation. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O3 chemistry cycle. Multi-spectral observations provide sensitivity to O3 in the lowermost troposphere, substantially reducing uncertainty in air quality predictions. TEMPO quantifies and tracks the evolution of aerosol loading. It provides near-real-time air quality products that will be made widely, publicly available. TEMPO will launch at a prime time to be the North American component of the global geostationary constellation of pollution monitoring together with European Sentinel-4 and Korean GEMS.

Remote sensing capabilities of the Airborne Compact Atmospheric Mapper

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 NASAs 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.

Evaluation of the Sensor Data Record from the nadir instruments of the Ozone Mapping Profiler Suite (OMPS)

This paper evaluates the first 15 months of the Ozone Mapping and Profiler Suite (OMPS) Sensor Data Record (SDR) acquired by the nadir sensors and processed by the National Oceanic and Atmospheric Administration Interface Data Processing Segment. The evaluation consists of an inter-comparison with a similar satellite instrument, an analysis using a radiative transfer model, and an assessment of product stability. This is in addition to the evaluation of sensor calibration and the Environment Data Record product that are also reported in this Special Issue. All these are parts of synergetic effort to provide comprehensive assessment at every level of the products to ensure its quality. It is found that the OMPS nadir SDR quality is satisfactory for the current Provisional maturity. Methods used in the evaluation are being further refined, developed, and expanded, in collaboration with international community through the Global Space-based Inter-Calibration System, to support the upcoming long-term monitoring.

High-resolution NO2 observations from the Airborne Compact Atmospheric Mapper: Retrieval and validation

Nitrogen dioxide (NO2) is a short-lived atmospheric pollutant that serves as an air quality indicator, and is itself a health concern. The Airborne Compact Atmospheric Mapper (ACAM) was flown on board the NASA UC-12 aircraft during the DISCOVER-AQ Maryland field campaign in July 2011. The instrument collected hyperspectral remote sensing measurements in the 304-910 nm range, allowing day-time observations of several tropospheric pollutants, including nitrogen dioxide (NO2), at an unprecedented spatial resolution of 1.5 × 1.1 km2. Retrievals of slant column abundance are based on the Differential Optical Absorption Spectroscopy (DOAS) method. For the Air Mass Factor (AMF) computations needed to convert these retrievals to vertical column abundance, we include high resolution information for the surface reflectivity by using bidirectional reflectance distribution function (BRDF) data from the Moderate Resolution Imaging Spectroradiometer (MODIS). We use high-resolution simulated vertical distributions of NO2 from the Community Multiscale Air Quality (CMAQ) and Global Modeling Initiative (GMI) models to account for the temporal variation in atmospheric NO2 to retrieve middle- and lower-tropospheric NO2 columns (NO2 below the aircraft). We compare NO2 derived from ACAM measurements with in-situ observations from NASAs P-3B research aircraft, total column observations from the ground-based Pandora spectrometers, and tropospheric column observations from the space-based OMI instrument. The high-resolution ACAM measurements not only give new insights into our understanding of atmospheric composition and chemistry through observation of sub-sampling variability in typical satellite and model resolutions, but they also provide opportunities for testing algorithm improvements for forthcoming geostationary air quality missions.

Analysis of ACAM Data for Trace Gas Retrievals during the 2011 DISCOVER-AQ Campaign

To improve the trace gas retrieval from Airborne Compact Atmospheric Mapper (ACAM) during the DSICOVER-AQ campaigns, we characterize the signal to noise ratio (SNR) of the ACAM measurement. From the standard deviations of the fitting residuals, the SNRs of ACAM nadir measurements are estimated to vary from ~300 at 310 nm to ~1000 in the blue spectral region; the zenith data are noisier due to reduced levels of illumination and lower system throughput and also show many more pixels with abrupt anomalous values; therefore, a new method is developed to derive a solar irradiance reference at the top of the atmosphere (TOA) from average nadir measurements, at instrument spectral resolution and including instrument calibration characteristics. Using this reference can significantly reduce fitting residuals and improve the retrievals. This approach derives an absolute reference for direct fitting algorithms involving radiative transfer calculations and thus can be applied to both aircraft and ground-based measurements. The comparison of ACAM radiance with simulations using coincident ozonesonde and OMI data shows large wavelength-dependent biases in ACAM data, varying from ~−19% at 310 nm to 5% at 360 nm. Correcting ACAM radiance in direct-fitting based ozone profile algorithm significantly improves the consistency with OMI total ozone.

The GeoTASO airborne spectrometer project

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.

OMPS early orbit dark and bias evaluation and calibration

The dark signal on an Ozone Mapper Profiler Suite (OMPS) charge-coupled device (CCD) results when electrons are thermally emitted into the conduction band of pixels in the active and storage regions. It effectively adds offsets to the photon-generated pixel counts and therefore impacts the Sensor Data Record (SDR) performance. This paper presents OMPS on-orbit results from dark current and electrical bias characterization and calibration on the system level. In particular, data from nominal and diagnostic activities has been collected and analyzed to extract general trends and features about the in-flight detector behaviors. The in-flight dark and bias signals are then compared with the prelaunch on-ground performance for each channel. The South Atlantic Anomaly (SAA) impact and temperature dependency are also addressed. The analysis results have demonstrated that the OMPS CCD performance successfully transferred from ground to orbit; the in-flight timing pattern of the nominal dark measurements are well suited to determine general dark currents of the individual pixels, and data collected during the early orbit calibration are sufficient to perform internal consistency checks of sensor dark and bias parameters and instrument behavior. Results also suggest that to minimize the influence of hot pixels and other effects of CCD lattice damage due to energetic particle hits, the dark current shall be updated on a daily basis rather than the weekly basis as planned.

Calibration of a radiance standard for the NPP/OMPS instrument

In June 2007, a spherical integrating source was calibrated in the National Aeronautics and Space Administration (NASA) Goddard Space Flight Centers (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 NISTs 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.

Retrievals from the Limb Ozone Retrieval Experiment on STS107

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 channels altitude scale, cloud top height and aerosol extinction. Also shown are a sub-set of flight data and the corresponding retrieved ozone profiles.