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NASA NTRS2020

Geophysical Retrievals During OLYMPEX/RADEX Using the Advanced Microwave Precipitation Radiometer

The Olympic Mountains Experiment and Radar Definition Experiment (OLYMPEX/RADEX) took place Fall 2015 – Spring 2016 in Washington, United States. The Advanced Microwave Precipitation Radiometer (AMPR) was flown on NASA ER-2 aircraft during science flights. This poster summarizes advancements in geophysical retrievals using AMPR data from OLYMPEX/RADEX. Calm ocean has low emissivity at microwave frequencies; wind creates foam – increases emissivity. Liquid hydrometeors in atmosphere generally yield higher brightness temperature (T(sub b)) due to their higher reflectance. Effect of liquid hydrometeors depends highly on frequency –resonance increases with increasing frequency, as does absorption (e.g., due to water vapor). Retrieve cloud liquid water (CLW), water vapor (WV), and 10-m wind speed (WS) using multiple T(sub b).

Amoit, Corey A.↗
NASA NTRS2000

A 3-D Model Analysis of The Impact of Asian Anthropogenic Emissions on the Sulfur Cycle Over the Pacific Ocean

The impact of anthropogenic activities on the SO2 and sulfate aerosol levels over the Pacific region is examined in the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model. We focus on the analysis of the data from the NASA Pacific Exploratory Missions (PEM) over the western North Pacific and the tropical Pacific. These missions include PEM-West A in September-October 1991, when the Asian outflow was at the minimum but the upper atmosphere was heavily influenced by the Pinatubo volcanic eruption, and PEM-West B in March-April 1994 when the Asian outflow was at the maximum, and PEM-Tropics A in August-September at a region relatively free of direct anthropogenic influences. Specifically, we will examine the relative importance of anthropogenic, volcanic and biogenic sources to the SO2 and sulfate concentrations over the Pacific, and quantify the processes controlling the distributions of SO2 and sulfate in both the boundary layer and the free troposphere. We will also assess the global impact of SO2 emission in Asia on the sulfate aerosol loading.

Chin, Mian↗
NASA NTRS2004

Transport of Biomass Burning Emissions from Southern Africa

The transport of biomass burning emissions from southern Africa to the neighboring Atlantic and Indian Oceans during the dry season (May-October) of 2000 is characterized using ground, ozonesonde, and aircraft measurements of carbon monoxide (CO) and ozone (O3) in and around southern Africa, together with the GEOS-CHEM global model of tropospheric chemistry. The model shows a positive bias of approximately 20% for CO and a negative bias of approximately 10-25% for O3 at oceanic sites downwind of fire emissions. Near areas of active fire emissions the model shows a negative bias of approximately 60% and approximately 30% for CO and O3, respectively, likely due to the coarse spatial (2 deg. x 2.5 deg.) and temporal (monthly) resolution of the model compared to that of active fires. On average, from 1994 to 2000, approximately 60 Tg of carbon monoxide (CO) from biomass burning in southern Africa was transported eastward to the Indian Ocean across the latitude band 0 deg. -60 S during the 6 months of the dry season. Over the same time period, approximately 40 Tg of CO from southern African biomass burning was transported westward to the Atlantic Ocean over the latitudes 0 deg. -20 S during the 6-month dry season, but most of that amount was transported back eastward over higher latitudes to the south (21 deg. -60 S). Eastward transport of biomass burning emissions from southern Africa enhances CO concentrations by approximately 4- 13 ppbv per month over the southern subtropical Indian Ocean during the dry season, with peak enhancements in September. Carbon monoxide from southern African and South American biomass burning is seen in the model simulations as far away as Australia, contributing approximately 8 ppbv and approximately 12-15 ppbv CO, respectively, and thus explaining the approximately 20- 25 ppbv observed enhancement of CO over Melbourne in mid-September 2000.

Sinha, Parikhit↗
NASA NTRSDate not supplied

Sunglint-aided Methane Retrieval: Using Sentinel-2 to Quantify Offshore Oil and Gas Emissions

The extraction, production, and transportation of oil and gas via activities such as intentional venting and fugitive emissions are leading contributors to anthropogenic methane emissions. Offshore operations comprise a significant percentage of all oil and gas operations, yet emission monitoring over the ocean is insufficient. Due to low surface reflectance over the ocean, remote sensing measurements offshore are limited. Therefore offshore contributions to the overall global methane budget are unknown. Regulators such as the Bureau of Ocean and Energy Management (BOEM) and the Bureau of Safety and Environmental Enforcement (BSEE) are unable to validate operator-reported methane emission estimates. The NASA DEVELOP Program partnered with BOEM, BSEE, and SkyTruth to identify potential offshore methane sources in the Gulf of Mexico. Drawing upon existing retrieval methods to detect and quantify onshore methane emissions (Varon et al., 2021), we selected sunglint scenes to detect methane plumes over the ocean in Sentinel-2 imagery. We detected two methane plumes at the Constitution complex in the Gulf of Mexico and off the coast of Pointe-Noire, Congo. If expanded, these methods could serve a vital role in validating operator reporting and quantifying climate impacts of offshore oil and gas operations - complementing those of next generation satellites.

Katherine Howell↗
NASA NTRS2021

Terra and Aqua MODIS Thermal Emissive Bands Calibration and RVS Stability Assessments Using an In Situ Ocean Target

MODIS, whose openly-public data have been used for over two decades to monitor and address global issues, has 16 Thermal Emissive Bands (TEBs) with central wavelengths that range from 3.7 μm to 14.4 μm, and are calibrated on-orbit using observations from its on-board blackbody. In order to maintain MODIS’ rich, well-calibrated archive of multispectral imagery and data, Earth targets are regularly used to track its long-term stability, as well as the consistency between the two sensors onboard the Terra and Aqua satellites. Moreover, these scenes can be used to compare MODIS Earth view data over the complete scan-angle range and evaluate the on-orbit performance of the TEBs response-versus-scan-angle (RVS) over mission lifetime. This manuscript focuses on evaluating the MODIS TEBs Collection (C6.1) radiometric calibration stability for both instruments using an in situ ocean target as reference (hereafter referred to as in situ sea surface temperature (SST)). Furthermore, it will assess the calibration consistency between the MODIS sensors. Lastly, it will analyze the on-orbit RVS stability for Terra and Aqua MODIS. Only cloud-free, nighttime MODIS TEB retrievals were used for the study. A normalization methodology is applied to standardize the MODIS data to the in situ SST. Additionally, spectral corrections were derived between some of the Terra and Aqua MODIS TEBs by using a combination of the MODIS Atmospheric Profile product and MODerate resolution atmospheric TRANsmission (MODTRAN) simulations. Results indicate that most MODIS TEBs exhibit mission-long trends of ±0.50 K – with Terra band 30 presenting the largest downward drift due to residual electronic cross-talk effects. Moreover, the calibration consistency analysis over a warm ocean target demonstrated that the average Terra-to-Aqua MODIS bias for most bands is well within ±0.50 K (bands 27 and 30 show the largest - electronic crosstalk-related - biases). Lastly, the MODIS TEBs RVS trends display changes of ±0.50 K (except for bands 25 and 27 at the end-of-scan angles) for both instruments. Overall, the MODIS TEBs remain well-calibrated and their RVSs aptly-characterized.

MODIS↗
NASA NTRS1985

Measurements of light background at large depth in the ocean

The mean intensity of Cerenkov emission from the products of K(40) decay and bioluminescence was measured at depths to 5 km. The intensity of ocean light background is found to depend upon depth and at the 5 km level is equal on averaged to 300 + or - 60 quanta/sq cms into spatial angle of 2 pi sterradian in transparency window. The amplitudes, duration and number of BL flashes were measured at various depths. The intensive flashes due to BL are shown to be observed rather seldom at depths over 4 km.

Bannykh, A. E.↗
NASA NTRS1988

The cycle of biogenic sulfur compounds over the Amazon Basin. I - Dry season

The concentrations of SO2, methylmercaptan, dimethylsulfide, H2S, aerosol sulfate, and methanesulfonate over the Amazon Basin during the July/August dry season were determined from samples collected by the NASA research aircraft. The results indicate that biogenic emissions represent an important, if not the dominant, source of sulfur to the atmosphere over Amazonia. Per unit area, the wet continental tropics appear to have about the same reduced sulfur emission flux as the oceanic area average (about 6 nmol/sq m per min), consistent with the fact that the aerosol sulfate concentration over the Amazon Basin is similar to the excess sulfate levels over the remote oceans. However, since the wet tropical continents represent only about 3 percent of the earth's surface, their global contribution is modest; it is also small relative to the anthropogenic emissions from fossil fuel burning.

Andreae, M. O.↗
NASA NTRSDate not supplied

Mapping Ocean-Reflected Radio Frequency Interference for the GPM Microwave Imager Using Normalized Retrieval Cost Function

By adapting an approach originally developed for WindSat, we identify regions where GMI is affected by radio frequency interference from ocean-reflected geostationary satellite emissions. Around North America, K-band emissions from geostationary satellites affect the GMI 18.7-GHz brightness temperatures, resulting in increases in the retrieval cost function. The method does not detect any 10.7-GHz RFI reflected of the ocean surrounding Europe. This study, which depends on the physically-based forward model for non-raining ocean retrievals, confirms results from a previous study that employed an empirical methodology.

Ian S. Adams↗
NASA NTRS1993

Polarimetric thermal emission from rough surfaces

Recent theoretical works have suggested the potential of passive polarimetry in the remote sensing of geophysical media. It was shown that the third Stokes parameter U of the thermal emission may become larger for azimuthally asymmetric fields of observation. In order to investigate the potential applicability of passive polarimetry to the remote sensing of ocean surface, measurements of the polarimetric thermal emission from a sinusoidal water surface and a numerical study of the polarimetric thermal emission from randomly rough ocean surfaces were performed. Measurements of sinusoidal water surface thermal emission were performed using a sinusoidal water surface which was created by placing a thin sheet of fiberglass with a sinusoidal profile in two dimensions extended infinitely in the third dimension onto a water surface. The theory of thermal emission from a 'two-layer' periodic surface is derived and the exact solution is performed using both the extended boundary condition method (EBC) and the method of moments (MOM). The theoretical predictions are found to be in good agreement with the experimental results once the effects of the radiometer antenna pattern are included and the contribution of background noise to the measurements is modeled. The experimental results show that the U parameter indicates the direction of periodicity of the water surface and can approach values of up to 30 K for the surface observed. Next, a numerical study of polarimetric thermal emission from randomly rough surfaces was performed. A Monte Carlo technique utilizing an exact method for calculating thermal emission was chosen for the study to avoid any of the limitations of the commonly used approximate methods in rough surface scattering. In this Monte Carlo technique, a set of finite rough surface profiles in two dimensions with desired statistics was generated and extended periodically. The polarimetric thermal emission from each surface of the set was then calculated using both the EBC and the MOM and the results were averaged. The surface statistics chosen were intended to model a wind perturbed ocean surface in the X to Ku band microwave region. The results indicate that the U parameter is sensitive to the azimuthal angle between the surface periodicity and the looking angle and to the rms height of the surface, and that the U parameter is fairly insensitive to variations in polar angle, permittivity, surface power law spectrum, and surface spectrum high frequency cutoff. These properties give further strength to the idea of using the U parameter to detect wind direction over the ocean.

Johnson, J. T.↗
NASA NTRS2016

New Methods for Retrieval of Chlorophyll Red Fluorescence from Hyperspectral Satellite Instruments: Simulations and Application to GOME-2 and SCIAMACHY

Global satellite measurements of solar-induced fluorescence (SIF) from chlorophyll over land and ocean have proven useful for a number of different applications related to physiology, phenology, and productivity of plants and phytoplankton. Terrestrial chlorophyll fluorescence is emitted throughout the red and far-red spectrum, producing two broad peaks near 683 and 736nm. From ocean surfaces, phytoplankton fluorescence emissions are entirely from the red region (683nm peak). Studies using satellite-derived SIF over land have focused almost exclusively on measurements in the far red (wavelengths greater than 712nm), since those are the most easily obtained with existing instrumentation. Here, we examine new ways to use existing hyperspectral satellite data sets to retrieve red SIF (wavelengths less than 712nm) over both land and ocean. Red SIF is thought to provide complementary information to that from the far red for terrestrial vegetation. The satellite instruments that we use were designed to make atmospheric trace-gas measurements and are therefore not optimal for observing SIF; they have coarse spatial resolution and only moderate spectral resolution (0.5nm). Nevertheless, these instruments, the Global Ozone Monitoring Instrument 2 (GOME-2) and the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY), offer a unique opportunity to compare red and far-red terrestrial SIF at regional spatial scales. Terrestrial SIF has been estimated with ground-, aircraft-, or satellite-based instruments by measuring the filling-in of atmospheric andor solar absorption spectral features by SIF. Our approach makes use of the oxygen (O2) gamma band that is not affected by SIF. The SIF-free O2 gamma band helps to estimate absorption within the spectrally variable O2 B band, which is filled in by red SIF. SIF also fills in the spectrally stable solar Fraunhofer lines (SFLs) at wavelengths both inside and just outside the O2 B band, which further helps to estimate red SIF emission. Our approach is then an extension of previous approaches applied to satellite data that utilized only the filling-in of SFLs by red SIF. We conducted retrievals of red SIF using an extensive database of simulated radiances covering a wide range of conditions. Our new algorithm produces good agreement between the simulated truth and retrievals and shows the potential of the O2 bands for noise reduction in red SIF retrievals as compared with approaches that rely solely on SFL filling. Biases seen with existing satellite data, most likely due to instrumental artifacts that vary in time, space, and with instrument, must be addressed in order to obtain reasonable results. Our 8-year record of red SIF observations over land with the GOME-2 allows for the first time reliable global mapping of monthly anomalies. These anomalies are shown to have similar spatiotemporal structure as those in the far red, particularly for drought-prone regions. There is a somewhat larger percentage response in the red as compared with the far red for these areas that are drought sensitive. We also demonstrate that good-quality ocean fluorescence line height retrievals can be achieved with GOME-2, SCIAMACHY, and similar instruments by utilizing the full complement of radiance measurements that span the red SIF emission feature.

spatiotemporal structure↗
NASA NTRS1992

DMS emissions from Sphagnum-dominated wetlands

The role of terrestrial sources of biogenic S and their effect on atmospheric chemistry remain as major unanswered questions in our understanding of the natural S cycle. The role of northern wetlands as sources and sinks of gaseous S was investigated by measuring rates of S gas exchange as a function of season, hydrologic conditions, and gradients in trophic status. Experiments were conducted in wetlands in New Hampshire (NH), and in Mire 239, a poor fen at the Experimental Lakes Area (ELA) in Ontario. Emissions were determined using Teflon enclosures, gas cryotrapping methods, and GC with flame photometric detection. Emissions of DMS dominated fluxes. In NH, DMS fluxes were greater than 1.6 micromol/m(sup -2)d(sup -1) in early summer, 1989 when temperatures were warm and the water table was approximately 5 cm below the surface. These rates are several-fold faster than average oceanic rates of DMS emission. A rapid drop in the water table resulted in a 6-fold decrease in DMS emissions in late July. In 1990, a new beaver dam kept water levels above the surface and S emissions were much lower than during 1989. The elimination of the beaver and a drop in the water table in August produced a rapid increase in S gas emissions. Emissions of DMS were highest in the most oligotrophic areas. Mire 239 (ELA) was irrigated with sulfuric and nitric acids to simulate acid rain. S emissions were determined before and after an acidification event in control and experimental areas in both minerotrophic and oligotrophic regions. Emissions of DMS were higher in the acidified areas compared to unacidified controls. Emissions were also much higher in the oligotrophic regions compared to the minerotrophic ones. Despite the wide differences in S gas fluxes (20-fold), it was difficult to determine whether acidification or variations in trophic status was not responsible for differences in S gas emissions. DMS emitted into the atmosphere was not derived from the water table but originated in peat in the unsaturated zone.

Hines, Mark E.↗
NASA NTRS1978

Remote sensing of rain over the ocean

Computer models of the microwave emission from the earth's atmosphere were used to study the problem of retrieving meteorological information from the SMMR instrument that will be flown on NIMBUS-G. Methods for retrieving rain rate, wind speed, cloud height, and ocean temperature are described for the case when the satellite is over the ocean.

Source record↗
NASA NTRS2021

Global Intercomparison of hyper-resolution ECOSTRESS coastal sea surface temperature measurements from the Space Station with VIIRS-N20

The ECOSTRESS multi-channel thermal radiometer on the Space Station has an unprecedented spatial resolution of 70 m and a return time of hours to 5 days. It resolves details of oceanographic features not detectable in imagery from MODIS or VIIRS, and has open-ocean coverage, unlike Landsat. We calibrated two years of ECOSTRESS sea surface temperature observations with L2 data from VIIRS-N20 (2019–2020) worldwide but especially focused on important upwelling systems currently undergoing climate change forcing. Unlike operational SST products from VIIRS-N20, the ECOSTRESS surface temperature algorithm does not use a regression approach to determine temperature, but solves a set of simultaneous equations based on first principles for both surface temperature and emissivity. We compared ECOSTRESS ocean temperatures to well-calibrated clear sky satellite measurements from VIIRS-N20. Data comparisons were constrained to those within 90 min of one another using co-located clear sky VIIRS and ECOSTRESS pixels. ECOSTRESS ocean temperatures have a consistent 1.01 ◦C negative bias relative to VIIRS-N20, although deviation in brightness temperatures within the 10.49 and 12.01 µm bands were much smaller. As an alternative, we compared the performance of NOAA, NASA, and U.S. Navy operational split-window SST regression algorithms taking into consideration the statistical limitations imposed by intrinsic SST spatial autocorrelation and applying corrections on brightness temperatures. We conclude that standard bias-correction methods using already validated and well-known algorithms can be applied to ECOSTRESS SST data, yielding highly accurate products of ultra-high spatial resolution for studies of biological and physical oceanography in a time when these are needed to properly evaluate regional and even local impacts of climate change.

Nicolas Weidberg↗
NASA NTRS1993

Atmospheric methyl bromide - Trends and global mass balance

A decadal time series of global CH3Br concentrations in the earth's atmosphere is presented. It is shown that average concentrations are about 10 pptv and during the last 4 yr may be increasing at 0.3 +/- 0.1 pptv/yr. It is estimated that the atmospheric lifetime of CH3Br that is due to reaction with OH is about 2 yr, which results in a calculated global emission rate of about 100 Gg/yr. Ocean supersaturations of 140-180 percent are observed, and atmospheric concentrations over the open oceans are higher than at comparably located coastal sites. The ocean source is estimated to be about 35 Gg/yr. The remaining emissions must come from other natural sources and anthropogenic activities.

Khalil, M. A. K.↗
NASA NTRS1993

Fluorescence of dissolved organic matter: A comparison of north Pacific and north Atlantic Oceans during April 1991

Profiles of airborne-laser-induced fluorescence emission from dissolved organic matter in the upper ocean have been produced and compared for the Southern California Bight (SCB) and the Mid-Atlantic Bight (MAB). Findings were as follows. (1) The fluorescent components of dissolved organic matter (FDOM) are present in easily measurable quantities from near shore to well over 300 km offshore in the SCB and are likewise easily measurable in the coastal, shelf, slope, and Gulf Stream waters of the MAB. (2) The reange of FDOM in the MAB is considerably greater than that in the SCB. (3) The lowest FDOM levels observed in the SCB were higher than those found in the Gulf Stream. (4) The onshore-to-offshore spatial gradient of the FDOM was found to be considerably lower in the SCB than in the MAB, with the highest levels of FDOM being found immediately adjacent to the coast in the MAB. This suggests that the water adjacent to the SCB shoreline is not as strongly influenced by terrestrial and estuarine sources of FDOM as the MAB is. (5) The spatial distribution of the FDOM within both the SCB and the MAB is frequently coherent with the spatial distribution of chlorophyll determined form the concurrent airborne- laser- induced phytoplankton pigment fluorescence measurements. However, distinct noncoherency is sometimes observed, especially at water mass boundaries.

Hoge, Frank E.↗
NASA NTRS1980

Passive microwave remote sensing of the ocean - A review

This paper reviews the current status of passive microwave remote sensing of the ocean. The physics of emission and instrumentation are highlighted in order to establish a relationship between the thermal emission and retrieved geophysical parameters. A discussion then follows on measurements of temperature, salinity, windspeed, etc. using passive microwave systems. These measurements are related to the accuracy and spatial resolution required by the users. The status of passive microwave remote sensing is summarized and recommendations for future research are presented.

Swift, C. T.↗
NASA NTRS1981

Moisture sounding at millimeter wavelengths /94/183 GHz/ at high altitudes

A moisture sounding radiometer at millimeter wavelengths has been developed for high altitude measurements onboard NASA's WB-57F aircraft. Three channels about the 183.3 GHz water vapor line permit measurement of the atmospheric water vapor profile. A single window channel at 94 GHz provides correction for clouds over the ocean and for surface emissivity variations over land. The instrument is an imaging radiometer operating under microprocessor control throughout each data flight. The system is contained within two packages integrated into the WB-57F pallet. A ground support system was used to perform a quick-look analysis of the data collected immediately following each flight.

Gagliano, J. A.↗
NASA NTRS1999

Sea Surface Slope Statistics for Intermediate and Shore Scale Ocean Waves Measured Using a Low-Altitude Aircraft

Ocean surface remote sensing techniques often rely on scattering or emission linked to shorter- scale gravity-capillary ocean wavelets. However, it is increasingly apparent that slightly longer wavelengths of O(10 to 500 cm) are vital components in the robust sea surface description needed to link varied global remote sensing data sets. This paper describes a sensor suite developed to examine sea surface slope variations in the field using an aircraft flying at very low altitude (below 30 m) and will also provide preliminary measurements detailing changes in slope characteristics versus sea state and friction velocity. Two-dimensional surface slope is measured using simultaneous range measurements from three compact short-range laser altimeters mounted in an equilateral triangle arrangement with spacing of about 1 m. In addition, all three lasers provide independent wave elevation profiles after GPS-aided correction for aircraft altitude. Laser range precision is 1 cm rms while vertical motion correction is 15 cm rms. The measurements are made along-track at approximately 1 m intervals setting the spatial scale of the measurement to cover waves of intermediate to long scale. Products available for this array then include surface elevation, two-dimensional slope distribution, and the cross- and along-track 1-D slope distributions. To complement the laser, a down-looking mm-wave radar scatterometer is centered within the laser array to measure radar backscatter simultaneously with the laser slope. The radar's footprint is nominally 1 m in diameter. Near-vertical radar backscatter is inversely proportional to the small-scale surface slope variance and to the tilt of the underlying (laser-measured) surface facet. Together the laser and radar data provide information on wave roughness from the longest scales down to about 1 cm. These measurements are complemented by aircraft turbulence probe data that provides robust surface flux information.

Vandemack, Douglas↗