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Laboratory measurements were performed to characterize the geometrical effects in the calibration of the NASA's cloud absorption radiometer (CAR). The measurements involved three integrating sphere sources (ISSs) operated at different light levels and experimental setups to determine radiance variability. The radiance gradients across the three ISS apertures were 0.2%-2.6% for different visible, near-infrared, and shortwave infrared illumination levels but OCIS codes: 120.5800, 120.3150, 120.5630, 120.0280, 110.1220, 110.6770.

The Ozone Monitoring Instrument (OMI) was launched on July 15, 2004 on the National Aeronautics and Space Administration's Earth Observing System Aura satellite. The OMI instrument is an ultraviolet-visible imaging spectrograph that uses two-dimensional charge-coupled device 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 the OMI design and discusses the main performance and calibration features and results. Index Terms--Calibration, charge coupled device (CCD), remote sensing, ultraviolet spectroscopy.

A primary goal of the Geostationary Operational Environmental Satellite R‐series Post Launch Test (GOES‐R PLT) Field Campaign during spring 2017 was the performance evaluation of the Geostationary Lightning Mapper (GLM) aboard the GOES‐16 satellite. The NASA Goddard Geo‐CAPE Airborne Simulator (GCAS), an ultra‐violet visible spectrometer, piggybacked on the aircraft mission to allow continuous hyper‐spectral measurements at high spectral and spatial resolutions simultaneously with optical lightning detection by the Fly's Eye GLM Simulator while overflying convective systems. NO2 columns retrieved from GCAS were used to estimate the moles of NOx produced per flash, referred to as lightning NOx production efficiency (LNOx PE) for convective systems over the United States and western Atlantic. The mean PE was determined to be 360 ± 180 mol per flash for optically detected GLM flashes and 230 ± 115 mol per flash for radio‐wave detected Earth Networks Total Lightning Network flashes. These values span the commonly cited range of 100–500 mol per flash for midlatitude flashes. LNOx PE was found to be positively correlated with GLM flash multiplicity and flash optical energy but negatively correlated with flash density. The positive correlations provide encouragement for PE parameterizations in terms of flash energy or multiplicity. Observations during the GOES‐R PLT field campaign provide a preview of the analysis that will be possible when continuous lightning detection is coupled with hourly NO2 columns from a geostationary instrument such as Tropospheric Emissions: Monitoring of Pollution. Plain Language Summary: A goal of the Geostationary Operational Environmental Satellite R‐series Post Launch Test (GOES‐R PLT) Field Campaign during spring 2017 was evaluation of the Geostationary Lightning Mapper (GLM) aboard the GOES‐16 satellite. The NASA Goddard Geo‐CAPE Airborne Simulator (GCAS) piggybacked on the aircraft allowing for continuous column measurements of NO2, a member of the nitrogen oxide family (NOx) that is also an ozone precursor. NO2 columns from GCAS were used to estimate the moles of NOx produced per lightning flash for 10 convective systems over the United States and western Atlantic. The moles of NOx produced per flash was determined to be approximately 360 mol per flash for optically detected GLM flashes and 230 mol per flash for radio‐wave detected Earth Networks Total Lightning Network flashes. These values span the commonly cited range of 100–500 mol per flash for midlatitude flashes. Observations during the GOES‐R PLT field campaign provide a preview of the analysis that will be possible when continuous lightning detection is coupled with NO2 columns from a geostationary instrument such as Tropospheric Emissions: Monitoring of Pollution. Key Points: NO2 columns from Goddard Geo‐CAPE Airborne Simulator are used to estimate NOx production per flashNOx production by lightning detected by the Geostationary Lightning Mapper over the United States is found to equal 360 mol per flashNOx production per flash is positively correlated with flash multiplicity and optical energy but negatively correlated with flash density [ABSTRACT FROM AUTHOR]

Nitrogen oxides (NOx = NO + NO2) play a crucial role in the formation of ozone and secondary inorganic and organic aerosols, thus affecting human health, global radiation budget, and climate. The diurnal and spatial variations of NO2 are functions of emissions, advection, deposition, vertical mixing, and chemistry. Their observations, therefore, provide useful constraints in our understanding of these factors. We employ a Regional chEmical and trAnsport model (REAM) to analyze the observed temporal (diurnal cycles) and spatial distributions of NO2 concentrations and tropospheric vertical column densities (TVCDs) using aircraft in situ measurements, surface EPA Air Quality System (AQS) observations, as well as the measurements of TVCDs by satellite instruments (OMI: the Ozone Monitoring Instrument; and GOME-2A: Global Ozone Monitoring Experiment - 2A), ground-based Pandora, and the Airborne Compact Atmospheric Mapper (ACAM) instrument, in July 2011 during the DISCOVER-AQ campaign over the Baltimore-Washington region. The model simulations at 36- and 4-km resolutions are in reasonably good agreement with the temporospatial NO2 observations in the daytime. However, nighttime mixing in the model needs to be enhanced to reproduce the observed NO2 diurnal cycle in the model. Another discrepancy is that Pandora measured NO2 TVCDs show much less variation in the late afternoon than simulated in the model. Relative to the 36-km model simulations, the 4-km model results show larger biases compared to the observations due largely to the larger spatial variations of NO2 in the model when the spatial resolution is increased from 36 to 4 km, although the biases are often comparable to the ranges of the observations. The high-resolution aircraft ACAM observations show a more dispersed distribution of NO2 vertical column densities (VCDs) and lower VCDs in urban regions than 4-km model simulations, reflecting likely the spatial distribution bias of NOx emissions in the National Emissions Inventory (NEI) 2011 at high resolution. [ABSTRACT FROM AUTHOR]

Abundant NO[sub 2] column measurements from airborne and ground-based Pandora spectrometers were collected as part of the 2018 Long Island Sound Tropospheric Ozone Study (LISTOS) in the New York City/Long Island Sound region and coincided with early measurements from the Sentinel-5P TROPOMI instrument. Both airborne- and ground-based measurements are used to evaluate the TROPOspheric Monitoring Instrument (TROPOMI) NO[sub 2] Tropospheric Vertical Column (TrVC) product v1.2 in this region, which has high spatial and temporal heterogeneity in NO[sub 2]. First, airborne and Pandora TrVCs are compared to evaluate the uncertainty of the airborne TrVC and establish the spatial representativeness of the Pandora observations. The 171 coincidences between Pandora and airborne TrVCs are found to be highly correlated (r[sup 2]=0.92 and slope of 1.03) with the biggest individual differences being associated with high temporal and/or spatial variability. These reference measurements (Pandora and airborne) are complementary with respect to temporal coverage and spatial representivity. Pandora spectrometers can provide continuous long-term measurements but may lack areal representivity when operated in direct-sun mode. Airborne spectrometers are typically only deployed for short periods of time, but their observations are more spatially representative of the satellite measurements with the added capability of retrieving at subpixel resolutions of 250 m × 250 m over the entire TROPOMI pixels they overfly. Thus, airborne data are more correlated with TROPOMI measurements (r[sup 2]=0.96) than Pandora measurements are with TROPOMI (r[sup 2]=0.84). The largest outliers between TROPOMI and the reference measurements are caused by errors in the TROPOMI retrieval of cloud pressure impacting the calculation of tropospheric air mass factors in cloud-free scenes. This factor causes a high bias in TROPOMI TrVCs of 4-11 %. Excluding these cloud-impacted points, TROPOMI has an overall low bias of 19-33% during the LISTOS timeframe of June-September 2018. Part of this low bias is caused by coarse a priori profile input from TM5-MP model; replacing these profiles with those from a 12 km NAMCMAQ analysis results in a 12-14 % increase in the TrVCs. Even with this improvement, the TROPOMI-NAMCMAQ TrVCs have a 7-19 % low bias, indicating needed improvement in a priori assumptions in the air mass factor calculation. Future work should explore additional impacts of a priori inputs to further assess the remaining low biases in TROPOMI using these datasets. [ABSTRACT FROM AUTHOR]

Satellite data from the Ozone Measuring Instrument (OMI) and Earth Polychromatic Imaging Camera (EPIC) for ozone amount and scene reflectivity (mostly from clouds) are used to study changes and global distribution of UV erythemal irradiance in mW/m² E(ζ,φ,z,t) and UV index (E/25 mWm²) over the Earth's surface as a function of latitude ζ, longitude φ, altitude z, and time t. OMI time series data starting in January 2005 to December 2018 are used to estimate 14-year changes in total column ozone TCO3 and scene reflectivity at 105 specific land plus 77 ocean locations in the Northern and Southern Hemispheres. Estimates of changes in atmospheric transmission T(ζ,φ,z,t) derived from cloud and haze reflectivity show almost no average 14-year change from 55° S to 35° N but show an increase from 40° N to 60° N. This implies increased solar insolation at high northern latitudes that suggests positive feedback for global warming. TCO3 has increased at a rate of 2% per decade for the latitudes between 60° S to 10° N changing to a decrease of 1% per decade between 40° N to 60° N. The result is an average decrease in E(ζ,φ,z,t) at a rate of 2% per decade in the Southern Hemisphere and an increase between 40° N to 60° N. For some specific sites (latitudes from 55° S to 45° N) there has been little or no change in E(ζ,φ,z,t) for the period 2005-2018. Nearly half the sites show the effects of both short- and long-term cloud change as well as total column ozone change. Synoptic EPIC data from the sunlit Earth are used derive ozone and reflectivity needed for global images of the distribution of E(ζ,φ,z,t) from sunrise to sunset centered on the Americas, Europe-Africa, and Asia. EPIC data are used to show the latitudinal distribution of E(ζ,φ,z,t) from the equator to 75° for specific longitudes. Dangerously high amounts of erythemal irradiance (12 < UV index < 18) are found for many low latitude and high-altitude sites (e.g., San Pedro, Chile (2.45 km), La Paz, Bolivia (3.78 km). Lower UV indices at some equatorial or high-altitude sites (e.g., Quito, Ecuador) are moderated by the presence of persistent cloud effects. High UVI levels (UVI > 6) are also found at most mid-latitude sites during the summer months. High levels of UVI are known to lead to health problems (skin cancer and eye cataracts) with extended unprotected exposures as shown in the extensive health statistics maintained by Australian Institute of Health and Welfare and the United States National Institute of Health National Cancer Institute. [ABSTRACT FROM AUTHOR]

NASA deployed an airborne UV/Visible spectrometer, GeoTASO, in May-June 2017 to produce high resolution (approximately 250 x 250 m), gapless NO2 datasets over the western shore of Lake Michigan and over the Los Angeles Basin. Results show that the airborne tropospheric vertical column retrievals compare well with ground-based Pandora spectrometer column NO2 observations (r² = 0.91 and slope of 1.03). Apparent disagreements between the two measurements can be sensitive to the coincidence criteria and are often associated with large local variability, including rapid temporal changes and also spatial heterogeneity that may be observed differently by the sunward viewing Pandora observations. The gapless mapping strategy executed during the 2017 GeoTASO flights provides data suitable for averaging to coarser areal resolutions to simulate satellite retrievals. As simulated satellite pixel area increases to values typical of TEMPO, TROPOMI, and OMI, the agreement with Pandora measurements is degraded as localized polluted plumes observed by Pandora are spatially averaged over larger areas (aircraft-to-Pandora slope: TEMPO scale = 0.88; TROPOMI scale = 0.77; OMI scale = 0.57). This behavior suggests that satellite products are representative of individual Pandora observations up to a certain pollution scale that depends on satellite spatial resolution. In these two regions, Pandora and TEMPO or TROPOMI have the potential to compare well up to pollution scales of 30 x 1015 molecules cm-2. Two publicly available OMI tropospheric NO2 retrievals are both found to be biased low with respect to Pandora observations (NASA V3 Standard Product slope = 0.18 and Berkeley High Resolution Product slope = 0.30). However, the agreement improves when higher resolution a priori inputs are used for the tropospheric air mass factor calculation. Overall, this work explores best practices for satellite validation strategies by showing the sensitivity to product spatial resolution and demonstrates how the high spatial resolution NO2 data retrieved from airborne spectrometers, such as GeoTASO, can be used with high temporal resolution surface observations to evaluate the influence of spatial heterogeneity on validation results. [ABSTRACT FROM AUTHOR]