Witthuhn J.,Leibniz Institute for Tropospheric Research |
Deneke H.,Leibniz Institute for Tropospheric Research |
MacKe A.,Leibniz Institute for Tropospheric Research |
Bernhard G.,Biospherical Instruments, Inc.
Atmospheric Measurement Techniques | Year: 2017
The 19-channel rotating shadowband radiometer GUVis-3511 built by Biospherical Instruments provides automated shipborne measurements of the direct, diffuse and global spectral irradiance components without a requirement for platform stabilization. Several direct sun products, including spectral direct beam transmittance, aerosol optical depth, Ångström exponent and precipitable water, can be derived from these observations. The individual steps of the data analysis are described, and the different sources of uncertainty are discussed. The total uncertainty of the observed direct beam transmittances is estimated to be about 4% for most channels within a 95% confidence interval for shipborne operation. The calibration is identified as the dominating contribution to the total uncertainty. A comparison of direct beam transmittance with those obtained from a Cimel sunphotometer at a land site and a manually operated Microtops II sunphotometer on a ship is presented. Measurements deviate by less than 3 and 4% on land and on ship, respectively, for most channels and in agreement with our previous uncertainty estimate. These numbers demonstrate that the instrument is well suited for shipborne operation, and the applied methods for motion correction work accurately. Based on spectral direct beam transmittance, aerosol optical depth can be retrieved with an uncertainty of 0.02 for all channels within a 95% confidence interval. The different methods to account for Rayleigh scattering and gas absorption in our scheme and in the Aerosol Robotic Network processing for Cimel sunphotometers lead to minor deviations. Relying on the cross calibration of the 940 nm water vapor channel with the Cimel sunphotometer, the column amount of precipitable water can be estimated with an uncertainty of ±0.034 cm. © Author(s) 2017.
Bernhard G.,Biospherical Instruments, Inc. |
Dahlback A.,University of Oslo |
Fioletov V.,Environment Canada |
Heikkila A.,Finnish Meteorological Institute |
And 4 more authors.
Atmospheric Chemistry and Physics | Year: 2013
Greatly increased levels of ultraviolet (UV) radiation were observed at thirteen Arctic and sub-Arctic ground stations in the spring of 2011, when the ozone abundance in the Arctic stratosphere dropped to the lowest amounts on record. Measurements of the noontime UV Index (UVI) during the low-ozone episode exceeded the climatological mean by up to 77% at locations in the western Arctic (Alaska, Canada, Greenland) and by up to 161% in Scandinavia. The UVI measured at the end of March at the Scandinavian sites was comparable to that typically observed 15-60 days later in the year when solar elevations are much higher. The cumulative UV dose measured during the period of the ozone anomaly exceeded the climatological mean by more than two standard deviations at 11 sites. Enhancements beyond three standard deviations were observed at seven sites and increases beyond four standard deviations at two sites. At the western sites, the episode occurred in March, when the Sun was still low in the sky, limiting absolute UVI anomalies to less than 0.5 UVI units. At the Scandinavian sites, absolute UVI anomalies ranged between 1.0 and 2.2UVI units. For example, at Finse, Norway, the noontime UVI on 30 March was 4.7, while the climatological UVI is 2.5. Although a UVI of 4.7 is still considered moderate, UV levels of this amount can lead to sunburn and photokeratitis during outdoor activity when radiation is reflected upward by snow towards the face of a person or animal. At the western sites, UV anomalies can be well explained with ozone anomalies of up to 41% below the climatological mean. At the Scandinavian sites, low ozone can only explain a UVI increase of 50-60 %. The remaining enhancement was mainly caused by the absence of clouds during the low-ozone period. © Author(s) 2013. CC Attribution 3.0 License.
Bais A.F.,Aristotle University of Thessaloniki |
McKenzie R.L.,NIWA - National Institute of Water and Atmospheric Research |
Bernhard G.,Biospherical Instruments, Inc. |
Aucamp P.J.,Ptersa Environmental Management Consultants |
And 3 more authors.
Photochemical and Photobiological Sciences | Year: 2015
We assess the importance of factors that determine the intensity of UV radiation at the Earth's surface. Among these, atmospheric ozone, which absorbs UV radiation, is of considerable importance, but other constituents of the atmosphere, as well as certain consequences of climate change, can also be major influences. Further, we assess the variations of UV radiation observed in the past and present, and provide projections for the future. Of particular interest are methods to measure or estimate UV radiation at the Earth's surface. These are needed for scientific understanding and, when they are sufficiently sensitive, they can serve as monitors of the effectiveness of the Montreal Protocol and its amendments. Also assessed are several aspects of UV radiation related to biological effects and health. The implications for ozone and UV radiation from two types of geoengineering methods that have been proposed to combat climate change are also discussed. In addition to ozone effects, the UV changes in the last two decades, derived from measurements, have been influenced by changes in aerosols, clouds, surface reflectivity, and, possibly, by solar activity. The positive trends of UV radiation observed after the mid-1990s over northern mid-latitudes are mainly due to decreases in clouds and aerosols. Despite some indications from measurements at a few stations, no statistically significant decreases in UV-B radiation attributable to the beginning of the ozone recovery have yet been detected. Projections for erythemal irradiance (UVery) suggest the following changes by the end of the 21st century (2090-2100) relative to the present time (2010-2020): (1) Ozone recovery (due to decreasing ozone-depleting substances and increasing greenhouse gases) would cause decreases in UVery, which will be highest (up to 40%) over Antarctica. Decreases would be small (less than 10%) outside the southern Polar Regions. A possible decline of solar activity during the 21st century might affect UV-B radiation at the surface indirectly through changes induced in stratospheric ozone. (2) The projected changes in cloud cover would lead to relatively small effects (less than 3%), except at northern high latitudes where increases in cloud cover could lead to decreases in UVery by up to 7%. (3) Reductions in reflectivity due to the melting of sea-ice in the Arctic would lead to decreases of UVery by up to 10%, while at the margins of the Antarctic the decreases would be smaller (2-3%). The melting of the sea-ice would expose the ocean surface formerly covered by ice to UV-B radiation up to 10 times stronger than before. (4) The expected improvement of air-quality and reductions of aerosols over the most populated areas of the northern hemisphere may result in 10-20% increases in UVery, except over China where even larger increases are projected. The projected aerosol effect for the southern hemisphere is generally very small. Aerosols are possibly the most important factor for future UV levels over heavily populated areas, but their projected effects are the most uncertain. © The Royal Society of Chemistry and Owner Societies 2015.
Hooker S.B.,NASA |
Morrow J.H.,Biospherical Instruments, Inc. |
Matsuoka A.,Laval University
Biogeosciences | Year: 2013
A next-generation in-water profiler designed to measure the apparent optical properties (AOPs) of seawater was developed and validated across a wide dynamic range of in-water properties. The new free-falling instrument, the Compact-Optical Profiling System (C-OPS), was based on sensors built with a cluster of 19 state-of-the-art microradiometers spanning 320-780 nm and a novel kite-shaped backplane. The new backplane includes tunable ballast, a hydrobaric buoyancy chamber, plus pitch and roll adjustments, to provide unprecedented stability and vertical resolution in near-surface waters. A unique data set was collected as part of the development activity plus the first major field campaign that used the new instrument, the Malina expedition to the Beaufort Sea in the vicinity of the Mackenzie River outflow. The data were of sufficient resolution and quality to show that errors - more correctly, uncertainties - in the execution of data sampling protocols were measurable at the 1% and 1 cm level with C-OPS. A theoretical sensitivity analysis as a function of three water types established by the peak in the remote sensing reflectance spectrum, Rrs(λ), revealed which water types and which parts of the spectrum were the most sensitive to data acquisition uncertainties. Shallow riverine waters were the most sensitive water type, and the ultraviolet and near-infrared spectral end members, which are critical to next-generation satellite missions, were the most sensitive parts of the spectrum. The sensitivity analysis also showed how the use of data products based on band ratios significantly mitigated the influence of data acquisition uncertainties. The unprecedented vertical resolution provided high-quality data products, which supported an alternative classification capability based on the spectral diffuse attenuation coefficient, Kd(λ). The Kd(320) and Kd(780) data showed how complex coastal systems can be distinguished two-dimensionally and how near-ice water masses are different from the neighboring open ocean. Finally, an algorithm for predicting the spectral absorption due to colored dissolved organic matter (CDOM), denoted αCDOM(λ), was developed using the Kd(320) /Kd(780) ratio, which was based on a linear relationship with respect to αCDOM(440). The robustness of the approach was established by expanding the use of the algorithm to include a geographically different coastal environment, the Southern Mid-Atlantic Bight, with no significant change in accuracy (approximately 98% of the variance explained). Alternative spectral end members reminiscent of next-generation (340 and 710 nm) as well as legacy satellite missions (412 and 670 nm) were also used to accurately derive αCDOM(440) from Kd(λ) ratios. © Author(s) 2013.
Bernhard G.,Biospherical Instruments, Inc.
Atmospheric Chemistry and Physics | Year: 2011
Spectral ultraviolet (UV) irradiance has been observed near Barrow, Alaska (71°N, 157° W) between 1991 and 2011 with an SUV-100 spectroradiometer. The instrument was historically part of the US National Science Foundation's UV Monitoring Network and is now a component of NSF's Arctic Observing Network. From these measurements, trends in monthly average irradiance and their uncertainties were calculated. The analysis focuses on two quantities, the UV Index (which is affected by atmospheric ozone concentrations) and irradiance at 345 nm (which is virtually insensitive to ozone). Uncertainties of trend estimates depend on variations in the data due to (1) natural variability, (2) systematic and random errors of the measurements, and (3) uncertainties caused by gaps in the time series. Using radiative transfer model calculations, systematic errors of the measurements were detected and corrected. Different correction schemes were tested to quantify the sensitivity of the trend estimates on the treatment of systematic errors. Depending on the correction method, estimates of decadal trends changed between 1.5% and 2.9%. Uncertainties in the trend estimates caused by error sources (2) and (3) were set into relation with the overall uncertainty of the trend determinations. Results show that these error sources are only relevant for February, March, and April when natural variability is low due to high surface albedo. This method of addressing measurement uncertainties in time series analysis is also applicable to other geophysical parameters. Trend estimates varied between-14% and +5% per decade and were significant (95.45% confidence level) only for the month of October. Depending on the correction method, October trends varied between-11.4% and-13.7% for irradiance at 345 nm and between-11.7% and-14.1% for the UV Index. These large trends are consistent with trends in short-wave (0.3-3.0 μm) solar irradiance measured with pyranometers at NOAA's Barrow Observatory and can be explained by a change in snow cover over the observation period: analysis of pyranometer data indicates that the first day of fall when albedo becomes larger than 0.6 after snow fall, and remains above 0.6 for the rest of the winter, has advanced with a statistically significant trend of 13.6 ± 9.7 days per decade. © 2011 Author(s).
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 737.55K | Year: 2016
The 14-DeCADES SBIR leverages the results of a FY13 spontaneous IRAD and a subsequent successful Phase 1 SBIR which characterized and tested key elements that will lead to a Phase 2 SBIR to design and build a commercial-off-the-shelf (COTS) multiwaveband sensor pair (radiance and irradiance) for airborne and shipboard sensing of ocean color in conditions of very low light. The new instruments will pair ruggedized, miniature photomultiplier tubes with silicon photodetectors to create so-called hybridnamic detectors, featuring 14 decades of linear dynamic range. The new radiometers will be suitable for making optical measurements of the atmosphere and ocean in low-light regimes wherein high-quality optical data are rarely available. Anticipated uses include improved calibration and validation data collection for next-generation NASA satellite missions emphasizing turbid atmospheres and waters. Basic research uses include twilight and nighttime diurnal or polar winter studies (e.g. aerosol optical depth from shadow band irradiance instruments), and other moon-lit measurements including airborne ocean color missions. While Phase 1 moved the prototype from a technology readiness level (TRL) of 3, to 4, the Phase 2 effort will advance the TRL of the new technology from a value of 4 to a value of 6 over the period of the SBIR Phase 2. This technology, known as LOLUX (Lowest Observable Light Upgraded XTRA class instruments), with irradiance (LOLUX-E) and radiance (LOLUX-L) sensors, will be supported with a portable, stabilized LED-based light source to insure that the sensors exhibit the desired stability during extended deployments. Following an extensive characterization period, this technology will be demonstrated in the field and delivered to NASA.
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 699.92K | Year: 2013
NASA has an ongoing commitment to collect in situ data with a documented uncertainty in keeping with established performance metrics for vicarious calibration of ocean color satellite sensors. This proposal seeks funding to develop an in-water "Hybridspectral" capability that combines two differing practices for data collection (multiwaveband and hyperspectral) to satisfy the diversity, accuracy, and precision requirements of future ocean color missions. Called the Compact Hybridspectral Radiometer (C-HyR), C-HyR places special focus on two important priorities from the call: 1) Instruments making measurements of the apparent optical properties; and 2) Hyperspectral radiometers (340 - 900 nm) for use in near-surface profiling. The C-HyR system leverages a 2004 NASA SBIR microradiometer development that lead to the Compact-Optical Profiling System (C-OPS), a commercially available multiwaveband radiometer system and adds a spectrograph-based upwelling Radiance Collector Assembly (RCA) for operations very near the surface of the water at the top of a vertical profile. In Phase II, attention will be paid to spectrograph selection with the goal of making optically valid measurements out to 900 nm, as requested in the call. For improved deployment security and shadow avoidance, the system uses an innovative buoyancy backplane with twin positioning thrusters to ensure ship avoidance and allow maneuvering the profiler to a desired sampling location. The result is an innovative expansion of existing state-of-the-art commercial instruments to include a spectral sampling capability that exceeds current and planned satellite requirements, and that can operate in optically complex near-shore regions. The benefits of this new sampling capability are an improved ability to separate the biotic and abiotic components of seawater, an improved ocean color mission calibration and validation capability into Case 2 waters, reduced deployment effort, and reduced deployment risks.
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 124.97K | Year: 2015
The 14-DeCADES SBIR leverages the results of a FY13 spontaneous IRAD to characterize and test (Phase 1) and subsequently design and build (Phase 2) a commercial-off-the-shelf (COTS) multiwaveband sensor for airborne sensing of ocean color in conditions of very low light. The new instrument will pair ruggedized, miniature photomultiplier tubes with silicon photodetectors to create so-called hybridnamic detectors for use in both radiance and irradiance radiometers, featuring 14 decades of linear dynamic range. The new radiometers will be suitable for making airborne optical measurements of the atmosphere and ocean in low-light regimes wherein high-quality optical data are rarely available. Anticipated uses include improved calibration and validation data collection for next-generation NASA satellite missions emphasizing turbid atmospheres and waters. Basic research uses include nighttime diurnal or polar winter studies (e.g. aerosol optical depth from shadow band irradiance instruments), and other moon-lit measurements including airborne ocean color missions. Phase 1 will leverage a technology readiness level (TRL) 3 prototype, bringing the work to TRL 4 during six months. If the Phase 2 work is successful, the activity will advance the TRL of the new instrument from a value of 3 (based on the IRAD prototype instrument) to a value of 6 over the period of the SBIR Phase 1 and 2. During Phase 1, necessary new fixturing and testing software and protocols will be developed, and a parallel engineering characterization of the IRAD prototype will confirm the instrument architecture. The resulting recommendations from the engineering tests will be used to establish the specifications for a Phase 2 sensor suite, to be proposed at the end of the project as a follow-on activity.
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 124.69K | Year: 2012
NASA has an ongoing commitment to collect in situ data with a documented uncertainty in keeping with established performance metrics for vicarious calibration of ocean color satellite sensors and to validate the algorithms for which the remotely-sensed observations are used as input parameters. This proposal seeks funding to develop an in-water "Hybridspectral" capability that combines two differing practices for data collection (multiwaveband and hyperspectral) to satisfy the necessary diversity, accuracy, and precision requirements of future ocean color missions. The result is an evolutionary upgrade of existing state-of-the-art commercial instruments to include spectral sampling capability exceeding current and planned satellite requirements and that operate in optically complex near-shore regions. The benefits of this new sampling capability are an improved ability to accurately separate the biotic and abiotic components of seawater, an improved ocean color mission calibration and validation capability into Case 2 waters, reduced deployment effort, and reduced deployment risks. This SBIR effort proposes to address a wide variety of these requirements with the development of a low-cost system called the Compact Hybridspectral Radiometer (C-HyR) with special focus on two important priorities from the call: 1)Instruments for oceanic, coastal, and fresh water measurements of apparent optical properties; and 2)Hyperspectral (340?900 nm) radiometers for use in near-surface profiling.
Agency: NSF | Branch: Continuing grant | Program: | Phase: | Award Amount: 653.12K | Year: 2012
The purpose of this project is to ensure continuation of UV observations at Barrow and Summit over the period 1-August 2012 ? 31-July 2015. These data include spectra of solar spectral irradiance between 280 and 600 nm, biologically effective dose-rates, total ozone, surface albedo, cloud optical depth, actinic flux, and photolysis rates for common reactions such as the photolysis of O3 and NO2. All data are made available via ACADIS, WOUDC, and NDACC. At Barrow, several key parameters affecting UV radiation such as snow cover and sea ice extent are changing rapidly. Extension of the climate data record (CDR) will provide a unique opportunity to study the effect of a changing environment on UV radiation. Measurements at Summit are ideally suited to probe the free troposphere and study the effects of long-range transport of pollutants and aerosols on UV radiation. The key intellectual merit of the proposed project centers on acquiring data that can be used to advance knowledge (1) of the present and future solar radiation climate of the Arctic and (2) of the factors that drive changes in the UV radiation. For example, by combining UV data with other measurements and modeling, parameterizations can be developed to predict future UV intensities and improve climate models (e.g., CCMs). Analysis of the long UV data record from Barrow will also help answering the ?SEARCH Question? whether the Arctic is moving to a new state. UV data are of importance for other AON projects and augment their intellectual merit. The broader impacts of this activity are to provide data to researchers in various disciplines, including satellite ground truthing, and to educators for use in science courses and curricula. The PIs intend to continue contributing to the NOAA Arctic Report Card and integrating the data into non-major courses at the university.