Marine-Atmospheric Emitted Radiance Interferometer Research Articles

Hyperspectral Infrared Observations of Arctic Snow, Sea Ice, and Non-Frozen Ocean from the RV Polarstern during the MOSAiC Expedition October 2019 to September 2020

This study highlights hyperspectral infrared observations from the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) collected as part of the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) deployment on the icebreaker RV Polarstern during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. The ARM M-AERI directly measures the infrared radiance emission spectrum between 520 cm−1 and 3000 cm−1 (19.2–3.3 μm) at 0.5 cm−1 spectral resolution. These ship-based observations provide a valuable set of radiance data for the modeling of snow/ice infrared emission as well as validation data for the assessment of satellite soundings. Remote sensing using hyperspectral infrared observations provides valuable information on sea surface properties (skin temperature and infrared emissivity), near-surface air temperature, and temperature lapse rate in the lowest kilometer. Comparison of the M-AERI observations with those from the DOE ARM meteorological tower and downlooking infrared thermometer are generally in good agreement with some notable differences. Operational satellite soundings from the NOAA-20 satellite were also assessed using ARM radiosondes launched from the RV Polarstern and measurements of the infrared snow surface emission from the M-AERI showing reasonable agreement.

Reducing Biases in Thermal Infrared Surface Radiance Calculations Over Global Oceans

Thermal infrared (IR) environmental satellite data assimilation and remote sensing of the surface and lower troposphere depend on accurate specification of the spectral surface emissivity within clear-sky forward calculations. Over ocean surfaces, accurate modeling of surface-leaving radiances over the sensor scanning swaths is complicated by a quasi-specular bidirectional reflectance distribution function (BRDF). Recent findings at the Joint Center for Satellite Data Assimilation (JCSDA) have also revealed significant zonally varying systematic biases (≈ |0.5| K) on a global scale over cold ocean waters, these the result of temperature dependence in the thermal IR optical constants. This paper proposes practical solutions to these problems by modeling thermal IR “effective emissivity” in a manner that accounts for both surface emission and quasi-specular reflectance, along with temperature dependence, while meeting the latency and computational constraints of operational global data assimilation and retrieval systems. We overview the theoretical basis of the model and validate it against ship-based Marine Atmospheric Emitted Radiance Interferometer (MAERI) spectra obtained from cold and warm water ocean campaigns.

The Impact of Nonzenith Elevation Angles on Ground-Based Infrared Thermodynamic Retrievals

Abstract Observing thermodynamic profiles within the planetary boundary layer is essential to understanding and predicting atmospheric phenomena because of the significant exchange of sensible and latent heat between the land and atmosphere within that layer. The Atmospheric Emitted Radiance Interferometer (AERI) is a ground-based infrared spectrometer used to obtain the vertical profiles of temperature and water vapor mixing ratio. Most AERIs are only capable of zenith views, although the Marine AERI (M-AERI) has a design that allows it to view various elevation angles. In this study, we quantify the improvement in the information content and accuracy of the retrieved profiles when nonzenith angles are included, as is common with microwave radiometer profilers. The impacts of the additional scan angles are quantified through both a synthetic study and with M-AERI observations from the ARM Cloud Aerosol Precipitation Experiment (ACAPEX) campaign. The simulation study shows that low elevation angles contain more information content for temperature whereas high elevation angles have more information content for water vapor. Outside of very humid environments, the addition of low elevation angles also results in lower root-mean-square errors when compared with high angles for both temperature and water vapor mixing ratio, although this is primarily a result of averaging multiple observations together to reduce instrument noise. Real-world results from the ACAPEX dataset indicate similar results as were found for the simulation study, although not all predicted benefits are realized because of the small sample size and observational uncertainties.

Accuracy Assessment of MERRA-2 and ERA-Interim Sea Surface Temperature, Air Temperature, and Humidity Profiles over the Atlantic Ocean Using AEROSE Measurements

AbstractSatellite and in situ measurements of the sea surface and the atmosphere often have inadequate sampling frequencies and often lack consistent global coverage. Because of such limitations, reanalysis model output is frequently used in atmospheric and oceanographic research endeavors to complement satellite and in situ data. The National Aeronautics and Space Administration’s (NASA’s) Goddard Earth Sciences Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) and the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim) datasets provide accurate, complete fields through the assimilation of many atmospheric and surface observations. Still, the reanalysis output data must be rigorously and continuously evaluated to understand their strengths and weaknesses. To this end, this study evaluates sea surface skin temperature (SSTskin) and atmospheric temperature and humidity profiles in MERRA-2 and ERA-Interim data through comparisons with independent Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) and radiosonde data from the Aerosols and Ocean Science Expeditions (AEROSE) cruises, focusing on the representation of spatial and temporal variability. SSTskinvalues are generally in good agreement with corresponding M-AERI measurements, with the average differences on the order of 0.1 K. Comparisons between MERRA-2 and ERA-Interim relative humidity and air temperature profiles with a total of 553 radiosondes that have been withheld from data assimilation schemes show good correspondence below 500 hPa: the average air temperature difference is <2 K and the average relative humidity discrepancy is within 10%. These results support the use of these MERRA-2 and ERA-Interim reanalysis fields in a variety of research applications.

Evaluation of the ERA5 Sea Surface Skin Temperature with Remotely-Sensed Shipborne Marine-Atmospheric Emitted Radiance Interferometer Data

Sea surface temperature is very important in weather and ocean forecasting, and studying the ocean, atmosphere and climate system. Measuring the sea surface skin temperature (SSTskin) with infrared radiometers onboard earth observation satellites and shipboard instruments is a mature subject spanning several decades. Reanalysis model output SSTskin, such as from the newly released ERA5, is very widely used and has been applied for monitoring climate change, weather prediction research, and other commercial applications. The ERA5 output SSTskin data must be rigorously evaluated to meet the stringent accuracy requirements for climate research. This study aims to estimate the accuracy of the ERA5 SSTskin fields and provide an associated error estimate by using measurements from accurate shipboard infrared radiometers: the Marine-Atmosphere Emitted Radiance Interferometers (M-AERIs). Overall, the ERA5 SSTskin has high correlation with ship-based radiometric measurements, with an average difference of~0.2 K with a Pearson correlation coefficient (R) of 0.993. Parts of the discrepancies are related to dust aerosols and variability in air-sea temperature differences. The downward radiative flux due to dust aerosols leads to significant SSTskin differences for ERA5. The SSTskin differences are greater with the large, positive air–sea temperature differences. This study provides suggestions for the applicability of ERA5 SSTskin fields in a selection of research applications.

Improving satellite retrieved night-time infrared sea surface temperatures in aerosol contaminated regions

Satellite retrievals of sea surface temperature (SST) have become necessary for many applications. Satellite infrared imaging radiometers passively measure the radiance emitted and reflected by the surface of the Earth and atmosphere. Tropospheric aerosols increase the signal attenuation at the satellite height, degrading the accuracy of SST retrievals. In this study to assess the infrared radiative effects of aerosols on satellite-derived skin SSTs (SSTskin), MODIS (MODerate-resolution Imaging Spectroradiometer) SSTskin retrievals are compared with quality-controlled, collocated SSTskin measurements from the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) deployed on research cruises during the Aerosols and Ocean Science Expeditions (AEROSE), and sub-surface temperatures measured by thermistors on drifting buoys. In this region, SSTskin retrievals from the MODIS on the Aqua satellite are generally much cooler than the in-situ measurements. In the Saharan outflow area between 90° W to 90° E and 20° S to 35° N where aerosol optical depths may be >0.5, satellite SSTskin are often >1 K cooler than the in situ data. The goal of this research is to determine the characteristics of aerosol effects on satellite retrieved infrared SST, and to derive formulae for improving accuracies of infrared-derived SSTs in aerosol-contaminated regions. A new method to derive a night-time Dust-induced SST Difference Index (DSDI) algorithm based on simulated brightness temperatures and Principal component (PC) analysis (PCA) at infrared wavelengths of 3.8, 8.9, 10.8 and 12.0 μm, was developed using radiative transfer simulations. The satellite SSTskin biases and standard deviations, derive by comparisons with coincident and collocated surface and in situ measurements, are reduced by 0.263 K and 0.166 K after the DSDI correction. This method can also improve the fraction of useful data available compared to the usual approach of discarding measurements identified as being contaminated by the effects of aerosols.

Retrieval of the Ocean Skin Temperature Profiles From Measurements of Infrared Hyperspectral Radiometers—Part II: Field Data Analysis

To obtain the vertical temperature profile of the thermal skin layer on the aqueous side of the ocean–atmosphere interface from radiance measurements of hyperspectral infrared radiometers, regularization methods are used to address the nonlinearity and ill-conditioning of the inverse problem associated with the retrieval. This paper demonstrates the truncated singular value decomposition regularization technique on field data sets obtained from the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI). The M-AERI takes highly accurate and spectrally resolved radiance measurements in the infrared, which allows for the sensing of temperature values within thermal skin layer depths of less than 1 mm below the ocean surface. Results showed temperature inversions found in the solution, but these are deemed unphysical, based on previous tests on synthetic data and by a scaling analysis using the Rayleigh number, which are presented here. The importance of sea surface emissivity for performing the atmospheric correction to M-AERI measurements to derive surface emissivity spectra is also discussed. The retrieved profiles exhibit a smooth exponential-like structure that agrees well with theory.

A Microbolometer Airborne Calibrated Infrared Radiometer: The Ball Experimental Sea Surface Temperature (BESST) Radiometer

A calibrated radiometer has been developed to enable the collection of accurate infrared measurements of sea surface temperature (SST) from unmanned aerial vehicles (UAVs). A key feature of this instrument is that in situ calibration is achieved with two built-in blackbodies (BBs). The instrument is designed so that the 2-D microbolometer array produces infrared images incremented as the aircraft travels, resulting in a well-calibrated strip of SST. Designed to be carried by medium-class UAVs, the Ball Experimental SST (BESST) instrument has been also successfully flown on manned aircraft. A recent intercalibration of BESST was carried out at the University of Miami using their National Institute of Standards and Technology traceable water-bath BB and a Fourier transform interferometer, the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI). The characterization of the BESST instrument with the Miami BB demonstrates the linearity and precision of the response of the microbolometer-based radiometer. Coincident measurements of SST from a nearby pier clearly demonstrated the excellent performance of the BESST instrument with a mean SST equal to that of the M-AERI and an RMS of 0.14 K very close to the microbolometer's advertised precision of 0.1 K. Cold calibration was not possible in Miami due to condensation, but a Ball BB was characterized relative to the Miami water-bath BB, and calibrations were made in Boulder at lower temperatures than were possible in Miami. The BESST instrument's performance remained linear, and the mean and RMS values did not change. UAV flights were conducted in summer/fall of 2013 over the Alaskan Arctic.

Radiometric measurements of ocean surface thermal variability

Measurements of diurnal temperature variability at the ocean surface have been available primarily from satellite Sea Surface Temperature (SST) retrievals and a small number of ship‐based radiometers. Since most areas are sampled from polar orbiting satellites at most twice a day, surface diurnal variability studies relied on theoretical modeling or extrapolation of results from in situ measurements at depth. The ocean surface responds very rapidly to changes in fluxes of heat and momentum, therefore diurnal variability at the ocean surface may be quite different than heating at depth. Measurements from the Marine Atmospheric Emitted Radiance Interferometer (M‐AERI) provide one of the few skin SST data sets augmented by ancillary measurements necessary for investigations into surface diurnal heating and cooling. This unique data set spans all major ocean basins and contains many days with diurnal warming. The timing of the peak in diurnal warming is directly related to the minimum wind speed and varies from 8:00 to 18:00 local‐mean‐time. Fluctuations in wind speed can result in multiple peaks in diurnal heating during a single afternoon. As wind speed increases, diurnal warming decreases (negatively correlated) and as insolation increases, diurnal warming increases (positively correlated). Changes in wind speed affect diurnal warming amplitudes very rapidly, while changes in insolation have a more gradual effect. The maximum correlation of wind speed (insolation) with changes in diurnal warming is at a time lag of 0 (50) min.

Comparisons of Shipboard Infrared Sea Surface Skin Temperature Measurements from the CIRIMS and the M-AERI

Abstract Extensive comparisons are made of the infrared sea surface skin temperature Tskin measured by the Calibrated Infrared In situ Measurement System (CIRIMS) and the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI). Data were collected from four separate deployments on the NOAA research vessel (R/V) Ronald H. Brown and the U.S. Coast Guard (USCG) Polar Sea over a wide range of latitudes and environmental conditions. The deployment time totaled roughly 6 months over a 4-yr period and resulted in over 7000 comparison values. The mean offset between the two instruments showed that CIRIMS consistently measured a lower temperature than the M-AERI, but by less than 0.10°C. This mean offset was found to be dependent upon sky condition, wind speed, and ship roll, which implies the offset is likely due to uncertainty in the emissivity. The CIRIMS Tskin was recomputed using two alterative emissivity values, one based on emissivity measured by the M-AERI and the other based on a wind-speed-dependent model. In both cases, the recomputation of the CIRIMS Tskin significantly reduced the mean offset. The overall standard deviation between the M-AERI and CIRIMS Tskin was 0.16°C, did not significantly depend on environmental conditions, and was within the expected values of instrument and comparison uncertainties. These comparisons demonstrate the success of CIRIMS in achieving good agreement with the M-AERI over a wide range of conditions. The results also highlight the importance of the sea surface emissivity when measuring the ocean surface skin temperature.

Integrated Ocean Skin and Bulk Temperature Measurements Using the Calibrated Infrared In Situ Measurement System (CIRIMS) and Through-Hull Ports

Abstract The design and performance of a shipboard-integrated system for underway skin and bulk temperature is presented. The system consists of the Calibrated Infrared In situ Measurement System (CIRIMS) and through-hull temperature sensors. The CIRIMS is an autonomous shipboard radiometer system that measures the sea surface skin temperature Tskin for validation of satellite-derived sea surface temperature products. General design considerations for shipboard radiometer systems are discussed and the philosophy behind the CIRIMS design is presented. Unique features of the design include a constant temperature housing to stabilize instrument drift, a two-point dynamic calibration procedure, separate sky- and sea-viewing radiometers for simultaneous measurements, and the ability to use an infrared transparent window for environmental protection. Laboratory testing and field deployments are used to establish an estimated error budget, which includes instrumentation and environmental uncertainties. The combination of this testing and field comparison to the Marine-Atmosphere Emitted Radiance Interferometer (M-AERI) and Infrared SST Autonomous Radiometer (ISAR) instruments indicates that the CIRIMS meets the design goal of ±0.10°C accuracy. Temperature and pressure sensors were installed in custom-designed through-hull ports on the NOAA research vessel (R/V) Ronald H. Brown and the University of Washington R/V Thomas G. Thompson to complement the CIRIMS measurements. The ports allow sensors to be installed while the ship is in water and can accommodate a variety of sensors. The combined system provides the ability to measure near-surface temperature profiles from the skin to a depth of 5 m while underway.

Profiling the Lower Troposphere over the Ocean with Infrared Hyperspectral Measurements of the Marine-Atmosphere Emitted Radiance Interferometer

Abstract Measurements of the spectra of infrared emission from the atmosphere were taken by a Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) deployed on the NOAA ship Ronald H. Brown during the Aerosol and Ocean Science Expedition (AEROSE) in the tropical Atlantic Ocean from 29 February to 26 March 2004. The spectra are used to retrieve profiles of temperature and humidity in the lower troposphere up to a height of 3000 m. The M-AERI retrievals of the atmospheric structure require an initial guess profile. In this work, retrievals obtained from four separate initializations are compared, using 1) radiosondes launched from the Ronald H. Brown, 2) NOAA/NWS/NCEP model reanalyses, 3) ECMWF model analyses, and 4) ECMWF model forecasts. The performance of the M-AERI retrievals for all four first-guess sources is then evaluated against the radiosonde measurements. The M-AERI retrievals initialized using radiosondes reproduce the radiosonde profiles quite well and capture much of the observed vertical structure as should be expected. Of the retrievals initialized with model fields, those obtained using the ECMWF data yielded results closest to the radiosonde observations and enabled detection of the Saharan air layer (SAL) evident during AEROSE. However, the NCEP reanalysis, as well as the corresponding retrievals, failed to detect the SAL. These results demonstrate the ability of the M-AERI profile retrievals to identify the anomalous humidity distributions in the lower troposphere, but underscore the need for suitable vertical resolution in the first-guess profile used in the retrievals under such conditions.

Ship‐based measurements for infrared sensor validation during Aerosol and Ocean Science Expedition 2004

This paper describes a unique validation data set acquired from a marine intensive observing period (IOP) conducted on board the NOAA Ship Ronald H. Brown (RHB) during the 2004 Aerosol and Ocean Science Expedition (AEROSE) in the tropical North Atlantic Ocean from 29 February to 26 March 2004. The radiometric and in situ data complement includes marine observations of the Saharan air layer (SAL), including two significant Saharan dust outbreaks over the Atlantic Ocean. Because the impact of tropospheric dust aerosols on satellite infrared (IR) radiometric observations has not yet been fully characterized, the AEROSE data are particularly valuable for IR sensor validation. Shipboard radiometric data germane to satellite validation include observations from a Marine Atmospheric Emitted Radiance Interferometer (M‐AERI), a Calibrated Infrared In situ Measurement System (CIRIMS), and Microtops handheld sunphotometers. Among other things, these data provide, for the first time, coincident IR spectra of the dry, dusty SAL from both the uplooking M‐AERI and the downlooking Atmospheric Infrared Sounder (AIRS) on board the Aqua satellite. In situ data collected throughout the cruise include Vaisala RS80/90 radiosondes, launched ≃3‐hourly to include Aqua overpass times. The Aqua matchup profiles provide data for validation of AIRS in the presence of high dust loading, along with temperature and water vapor profile retrievals of the SAL. The frequency of sonde launches also enables validation of coincident uplooking M‐AERI boundary layer profile retrievals. Preliminary analyses of the AEROSE data are presented here. Focused AEROSE validation studies are the subjects of separate papers.

The accuracy of the AATSR sea surface temperatures in the Caribbean

The Along-Track Scanning Radiometer (ATSR) series of instruments provides the means to obtain accurate measurements of sea surface temperature (SST), with a target total uncertainty of ± 0.3 K, 1 σ. In this paper, we present validation results from 1 year of comparisons between 1 km resolution SSTs derived from the third instrument in the series, the Advanced ATSR (AATSR), and in situ measurements obtained during 2003 from the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) over the Caribbean. Our dataset consists of 99 cloud-free matchups, 25 of which are two-channel SST retrievals (daytime) and 74 three-channel SST retrievals (nighttime). Validation results for both dual- and nadir-view SSTs for these matchups are presented. We demonstrate that the dual–nadir SST measurement difference (D–N) can be used to classify matchups and attribute the likely cause of a particularly high D–N to outbreaks of Saharan dust. Under conditions of ‘normal’ D–N, the bias and standard deviation of the two- and three-channel dual-view retrievals is − 0.05 K and 0.26 K, and 0.02 K and 0.25 K, respectively. Dual-view SSTs obtained when the D–N is high over the Caribbean exhibit significant warm biases of 0.60 K and 0.32 K for two- and three-channel retrievals, respectively. Cool biases, with respect to the bias for ‘normal’ D–N, are observed in the nadir three-channel (N3) SSTs; for matchups with high D–N, the bias and standard deviation are − 0.16 K and 0.31 K, compared with 0.14 K and 0.24 K for ‘normal’ D–N. The distribution of the nadir two-channel retrievals is non-Gaussian and the apparent accuracy is comparatively poor, demonstrating clearly the advantages of using a sensor with dual-viewing capabilities to obtain a superior atmospheric correction, particularly when data from an additional short-wave infrared channel (e.g. at 3.7 μm) is not available.

Near‐surface ocean temperature

The first open ocean deployment of the Skin Depth Experimental Profiler (SkinDeEP) was from the R/V Melville in the Gulf of California during the Marine Optical Characterization Experiment (MOCE‐5). SkinDeEP is an autonomous, vertical profiler for the upper few meters of the ocean. During MOCE‐5, SkinDeEP was deployed on ten separate occasions, and profiles were made at intervals of approximately 1 min each. A total of 976 profiles was acquired during the cruise. The ocean skin temperatures were measured by the Marine Atmosphere Emitted Radiance Interferometer (M‐AERI), an infrared spectroradiometer. Typical meteorological conditions were of low winds and high insolation. The data set provided captures the near‐surface temperature structure that decouples the skin layer from the conventional in situ bulk sea surface temperature (SST) measurements made at a depth of a few meters. Data from SkinDeEP showed strong diurnal warming within the upper few meters, with one extreme case of 4.6 K. There were large discrepancies when computing the skin‐bulk temperature difference with bulk temperatures at different depths. Results also show the strong dependency of the SST on air‐sea heat flux estimates, with warm‐layer errors of almost 60 Wm−2 associated with intense stratification. This indicates the importance of the inclusion of the skin temperature for accurate calculation of latent, sensible, and net longwave heat fluxes.

Infrared Interferometric Measurements of the Near-Surface Air Temperature over the Oceans

Abstract The radiometric measurement of the marine air temperature using a Fourier transform infrared spectroradiometer is described. The measurements are taken by the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) that has been deployed on many research ships in a wide range of conditions. This approach is inherently more accurate than conventional techniques and can be used to determine some of the error characteristics of the standard measurements. Examples are given from several cruises ranging from the Arctic to the equatorial Pacific Oceans. It is shown that the diurnal heating signal in radiometric air temperatures in the tropical Pacific can typically reach an amplitude of ∼15% of that measured by conventional sensors. Conventional data have long been recognized as being contaminated by direct solar heating and heat island effects of the ships or buoys on which they are mounted, but here this effect is quantified by comparisons with radiometric measurements.

Observations of large aerosol infrared forcing at the surface

Studies of aerosol effects on the Earth’s energy budget usually consider only the cooling effects at short (solar) wavelengths, but we demonstrate that they also have important warming effects at thermal infrared (IR) wavelengths that have rarely been observed and are commonly ignored in climate models. We use high‐resolution spectra to obtain the IR radiative forcing at the surface for aerosols encountered in the outflow from northeastern Asia. The spectra were measured by the Marine‐Atmospheric Emitted Radiance Interferometer (M‐AERI) from the NOAA Ship Ronald H. Brown during the Aerosol Characterization Experiment‐Asia (ACE‐Asia). We show that the daytime surface IR forcing are often a few Wm−2 and can reach almost 10 Wm−2 for large aerosol loadings. Thus, even the smaller aerosol IR forcing observed here are comparable to or greater than the 1 to 2 Wm−2 IR surface enhancement from increases in greenhouse gases. These results highlight the importance of aerosol IR forcing which should be included in climate model simulations.

Radiometric measurements of the sea-surface skin temperature: the competing roles of the diurnal thermocline and the cool skin

It has long been recognized that satellite-borne infrared radiometers measure radiance that is more closely related to the temperature of the skin of the ocean than the sub-surface bulk temperature, but, historically, atmospheric correction algorithm derivation and validation exercises have been conducted using bulk temperatures measured at a depth of a metre or more. A recent validation of sea-surface temperature (SST) fields derived from the Advanced Very High Resolution Radiometer (AVHRR) with skin temperature measurements of the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) revealed a very low mean bias error, much smaller than was expected, given the thermal skin effect which acts to cool the surface with respect to sub-surface values by several tenths of a degree. This result does not imply the skin effect is unimportant-its effect is now well documented in many datasets-but that its effect is being partially compensated by diurnal heating effects. The evidence for this is presented and the consequences in terms of validating satellite-derived SSTs and of merging data from sensors with different satellite overpass times are discussed.

The Marine-Atmospheric Emitted Radiance Interferometer: A High-Accuracy, Seagoing Infrared Spectroradiometer

Abstract The Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) is described, and some examples of the environmental variables that can be derived from its measurements and the types of research that these can support are briefly presented. The M-AERI is a robust, accurate, self-calibrating, seagoing Fourier-transform interferometric infrared spectroradiometer that is deployed on marine platforms to measure the emission spectra from the sea surface and marine atmosphere. The instrument works continuously under computer control and functions well under a very wide range of environmental conditions with a high rate of data return. Spectral measurements are made in the range of ∼3 to ∼18 μm wavelength and are calibrated using two internal, National Institute of Standards and Technology–traceable blackbody cavities. The environmental variables derived from the spectra include the surface skin temperature of the ocean, surface emissivity, near-surface air temperature, and profiles of temperature and h...

Quasi-specular model for calculating the reflection of atmospheric-emitted infrared radiation from a rough water surface

A numerical model is developed for computation of the reflection of atmospheric-emitted IR radiance from a wind-roughened water body. The model assumes the Kirchhoff approximation for rough surface scattering. This allows application of the postulates of geometrical optics to determine the reflection of rays from an ensemble of wave facets. We performed the hemispherical integration with Gaussian quadrature by using an uplooking fast transmittance model. This calculation is simplified further through the concept of a reflection-diffusivity angle. The model compares favorably with observed radiance spectra obtained from the Marine-Atmospheric Emitted Radiance Interferometer during the Combined Sensor Program research cruise.