scholarly journals Reanalysis of the 1992 South Pole Millimetre-Wavelength Atmospheric Opacity Data

2004 ◽  
Vol 21 (3) ◽  
pp. 264-274 ◽  
Author(s):  
Richard A. Chamberlin
Keyword(s):  
Time Series ◽  
Transfer Model ◽  
South Pole ◽  
Millimetre Wave ◽  
Atmospheric Opacity ◽  
Site Survey ◽  
Direct Measurements ◽  
Gain Error ◽  
Sky Brightness ◽  
Total Opacity

AbstractIn 1992 an NRAO 225-GHz site survey heterodyne radiometer was placed at the Geographical South Pole. The instrument operated over an entire annual cycle and provided direct measurements of the millimetre-wave sky brightness temperature as a function of zenith angle. Interpreted in a single-slab ‘skydip’ radiation transfer model of the atmosphere, these sky brightness measurements provided a time series of the millimetre atmospheric opacity. Statistics derived from this opacity time series were important for making comparisons with other candidate millimetre and sub-millimetre wave astronomy sites. This paper reexamines the 1992 measurements and the original analysis. Details of the skydip fit model, radiometer gain error, instrument stability, and a mid-season replacement to a window in the instrument enclosure combined to cause a modest under-reporting of the atmospheric opacity in previous reports. Unchanged are earlier conclusions that dry air makes a significant contribution to the total opacity at 225 GHz.

scholarly journals Snow Stratigraphic Record at South Pole: Potential for Paleoclimatic Reconstruction

1985 ◽  
Vol 7 ◽  
pp. 26-33 ◽  
Author(s):  
E. Mosley-Thompson ◽  
P.D. Kruss ◽  
L.G. Thompson ◽  
M. Pourchet ◽  
P. Grootes
Keyword(s):  
Time Series ◽  
Temporal Resolution ◽  
Time Scale ◽  
Ice Core ◽  
Climatic Conditions ◽  
South Pole ◽  
Accumulation Rates ◽  
Geochemical Parameters ◽  
Absolute Dating ◽  
Oxygen Isotopic

An extensive investigation of the visible stratigraphy, microparticle concentration, liquid conductivity, oxygen isotopes and beta-radioactivity was conducted in pits excavated at Amundsen-Scott South Pole station. The objectives of the investigation were to assess the spatial representativeness of the geochemical and physical records preserved within the snow strata and to ascertain the temporal resolution which can be obtained from such ice-core records. Accurate interpretation of the time scale and reconstruction of climatic conditions from these time series requires (1) the analysis of as many stratigraphic parameters as possible and (2) the synthesis of data from a suite of cores in the study area. For periods of 10 a or less, regionally representative accumulation rates cannot be obtained from annual accumulation time series reconstructed at a single site. Although the microparticle concentrations, liquid conductivity and oxygen isotopic abundances all exhibit a seasonal cycle in the firn, the construction of an accurate time scale requires all three parameters in conjunction with the beta-radioactivity. Absolute dating will be impossible for cores from South Pole where entire accumulation years may be missing. Nevertheless, for East Antarctica, where accumulation rates are low (<0.1 m a−1 water equivalent), the good temporal resolution and the preservation of a distinct annual signal in some geochemical parameters makes the South Pole a very attractive site for deep ice-core drilling.

Exploring continuous time series of vegetation hyperspectral reflectance and solar-induced fluorescence through radiative transfer model inversion

2020 ◽  
Author(s):  
Marco Celesti ◽  
Khelvi Biriukova ◽  
Petya K. E. Campbell ◽  
Ilaria Cesana ◽  
Sergio Cogliati ◽  
...  
Keyword(s):  
Time Series ◽  
Radiative Transfer ◽  
Near Infrared ◽  
Plant Traits ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Optimization Approach ◽  
Ancillary Data ◽  
Full Spectrum ◽  
Retrieval Scheme

&lt;p&gt;Remote sensing of solar-induced chlorophyll fluorescence (SIF) is of growing interest for the scientific community due to the inherent link of SIF with vegetation photosynthetic activity. An increasing number of in situ and airborne fluorescence spectrometers has been deployed worldwide to advance the understanding and usage of SIF for ecosystem studies. Particularly, a number of sites has been instrumented with the FloX (J&amp;B Hyperspectral Devices, Germany), an automated instrument that houses two high resolution spectrometers covering the visible and near infrared spectral regions, one specifically optimized for fluorescence retrieval, the other for plant trait estimation.&lt;/p&gt;&lt;p&gt;In this contribution we explore the feasibility to consistently retrieve plant traits and SIF from canopy level FloX measurements through the numerical inversion of a light version of the SCOPE model. The optimization approach was specifically adapted to work with the high- frequency time series produced by the FloX. In this context, a strategy for optimal retrieval of plant traits at daily scale is discussed, together with the implementation of an emulator of the radiative transfer model in the retrieval scheme. The retrieval strategy was applied to site measurements across Europe and the US that span a variety of natural and agricultural ecosystems.&lt;/p&gt;&lt;p&gt;The full spectrum of canopy SIF, the fluorescence quantum efficiency, and main plant traits controlling light absorption and reabsorption were retrieved concurrently and evaluated over the growing season in comparison with site-specific ancillary data. Improvements and challenges of this method compared to other retrievals are discussed, together with the potential of applying a similar retrieval scheme to airborne datasets acquired with e.g. the HyPlant sensor, or the reconfigured &amp;#8220;FLEX mode&amp;#8221; data acquired with the recently launched Sentinel-3B during its commissioning phase.&lt;/p&gt;

Dynamics of a subglacial meltwater plume revealed by continuous subsurface monitoring directly on the calving front

2020 ◽  
Author(s):  
Evgeny A. Podolskiy ◽  
Naoya Kanna ◽  
Shin Sugiyama
Keyword(s):  
Time Series ◽  
Sampling Interval ◽  
Outburst Flood ◽  
Direct Measurements ◽  
Science Community ◽  
Temperature And Pressure ◽  
Glacial Lake Outburst Flood ◽  
Subsurface Monitoring ◽  
Subglacial Meltwater ◽  
Temperature Depth

&lt;p&gt;Recent literature has highlighted the great importance of subglacial meltwater plumes in a variety of processes including subaqueous ice melting, enhanced fjord-scale circulation, nutrient and heat mixing, foraging ground formation, and the movements of seals that apparently use plumes for returning to the sea surface.&lt;/p&gt;&lt;p&gt;However, direct measurements of plume water properties are scarce due to the difficulty of conducting observations near unstable glacier calving fronts. A few studies have succeeded in obtaining snapshot views of plume structures using bio-logging, remotely operated vessels, or helicopter-borne eXpendable Conductivity Temperature Depth (XCTD) probes, but continuous data time-series remain elusive and technically challenging.&lt;/p&gt;&lt;p&gt;In this study, we overcame these limitations by deploying mooring-based equipment between major calving events from a calving front of Bowdoin Glacier, an ocean-terminating glacier in Northwest Greenland. In July 2017, a first-of-its-kind 10 d dataset of plume dynamics was obtained by attaching instruments to the ice cliff for the logging of conductivity, temperature, and pressure at depths of ~5 m and ~100 m, with a sampling interval of 10 s.&lt;/p&gt;&lt;p&gt;Nonlinear and spectral time-series analysis revealed a chaotic system, an extremely turbulent environment, the presence of coherent structures, tide-modulated signals, and a non-intuitive transition in the dynamics of the plume due to a witnessed glacial lake outburst flood. Our observations should provide an important reference for the glacier-science community, including modellers interested in the evolution of ocean-terminating glaciers, fjord-scale circulation, and glacier fjord ecosystems.&lt;/p&gt;

scholarly journals Exploring the observational constraints on the simulation of brown carbon

2018 ◽  
Vol 18 (2) ◽  
pp. 635-653 ◽  
Author(s):  
Xuan Wang ◽  
Colette L. Heald ◽  
Jiumeng Liu ◽  
Rodney J. Weber ◽  
Pedro Campuzano-Jost ◽  
...  
Keyword(s):  
Optical Properties ◽  
Transport Model ◽  
Model Simulation ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Observational Constraints ◽  
Aircraft Measurements ◽  
Radiative Effect ◽  
Brown Carbon ◽  
Direct Measurements

Abstract. Organic aerosols (OA) that strongly absorb solar radiation in the near-UV are referred to as brown carbon (BrC). The sources, evolution, and optical properties of BrC remain highly uncertain and contribute significantly to uncertainty in the estimate of the global direct radiative effect (DRE) of aerosols. Previous modeling studies of BrC optical properties and DRE have been unable to fully evaluate model performance due to the lack of direct measurements of BrC absorption. In this study, we develop a global model simulation (GEOS-Chem) of BrC and test it against BrC absorption measurements from two aircraft campaigns in the continental US (SEAC4RS and DC3). To the best of our knowledge, this is the first study to compare simulated BrC absorption with direct aircraft measurements. We show that BrC absorption properties estimated based on previous laboratory measurements agree with the aircraft measurements of freshly emitted BrC absorption but overestimate aged BrC absorption. In addition, applying a photochemical scheme to simulate bleaching/degradation of BrC improves model skill. The airborne observations are therefore consistent with a mass absorption coefficient (MAC) of freshly emitted biomass burning OA of 1.33 m2 g−1 at 365 nm coupled with a 1-day whitening e-folding time. Using the GEOS-Chem chemical transport model integrated with the RRTMG radiative transfer model, we estimate that the top-of-the-atmosphere all-sky direct radiative effect (DRE) of OA is −0.344 Wm−2, 10 % higher than that without consideration of BrC absorption. Therefore, our best estimate of the absorption DRE of BrC is +0.048 Wm−2. We suggest that the DRE of BrC has been overestimated previously due to the lack of observational constraints from direct measurements and omission of the effects of photochemical whitening.

scholarly journals The meteorology and chemistry of high nitrogen oxide concentrations in the stable boundary layer at the South Pole

2018 ◽  
Vol 18 (5) ◽  
pp. 3755-3778 ◽  
Author(s):  
William Neff ◽  
Jim Crawford ◽  
Marty Buhr ◽  
John Nicovich ◽  
Gao Chen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Nitrogen Oxide ◽  
Stable Boundary Layer ◽  
Early Summer ◽  
Late Spring ◽  
Small Scale ◽  
South Pole ◽  
Stable Boundary ◽  
Direct Measurements ◽  
The Antarctic

Abstract. Four summer seasons of nitrogen oxide (NO) concentrations were obtained at the South Pole (SP) during the Sulfur Chemistry in the Antarctic Troposphere (ISCAT) program (1998 and 2000) and the Antarctic Tropospheric Chemistry Investigation (ANTCI) in (2003, 2005, 2006–2007). Together, analyses of the data collected from these studies provide insight into the large- to small-scale meteorology that sets the stage for extremes in NO and the significant variability that occurs day to day, within seasons, and year to year. In addition, these observations reveal the interplay between physical and chemical processes at work in the stable boundary layer of the high Antarctic plateau. We found a systematic evolution of the large-scale wind system over the ice sheet from winter to summer that controls the surface boundary layer and its effect on NO: initially in early spring (Days 280–310) the transport of warm air and clouds over West Antarctica dominates the environment over the SP; in late spring (Days 310–340), the winds at 300 hPa exhibit a bimodal behavior alternating between northwest and southeast quadrants, which is of significance to NO; in early summer (Days 340–375), the flow aloft is dominated by winds from the Weddell Sea; and finally, during late spring, winds aloft from the southeast are strongly associated with clear skies, shallow stable boundary layers, and light surface winds from the east – it is under these conditions that the highest NO occurs. Examination of the winds at 300 hPa from 1961 to 2013 shows that this seasonal pattern has not changed significantly, although the last twenty years have seen an increasing trend in easterly surface winds at the SP. What has also changed is the persistence of the ozone hole, often into early summer. With lower total ozone column density and higher sun elevation, the highest actinic flux responsible for the photolysis of snow nitrate now occurs in late spring under the shallow boundary layer conditions optimum for high accumulation of NO. This may occur via the non-linear HOX–NOx chemistry proposed after the first ISCAT field programs and NOx recycling to the surface where quantum yields may be large under the low-snow-accumulation regime of the Antarctic plateau. During the 2003 field program a sodar made direct measurements of the stable boundary layer depth (BLD), a key factor in explaining the chemistry of the high NO concentrations. Because direct measurements were not available in the other years, we developed an estimator for BLD using direct observations obtained in 2003 and step-wise linear regression with meteorological data from a 22 m tower (that was tested against independent data obtained in 1993). These data were then used with assumptions about the column abundance of NO to estimate surface fluxes of NOx. These results agreed in magnitude with results at Concordia Station and confirmed significant daily, intraseasonal and interannual variability in NO and its flux from the snow surface. Finally, we found that synoptic to mesoscale eddies governed the boundary layer circulation and accumulation pathways for NO at the SP rather than katabatic forcing. It was the small-scale features of the circulation including the transition from cloudy to clear conditions that set the stage for short-term extremes in NO, whereas larger-scale features were associated with more moderate concentrations.

scholarly journals Indirect measurement of anterior-posterior ground reaction forces using a minimal set of wearable inertial sensors: From healthy to hemiparetic walking

2020 ◽  
Author(s):  
Dheepak Arumukhom Revi ◽  
Andre Alvarez ◽  
Conor J. Walsh ◽  
Stefano M. M. De Rossi ◽  
Louis N Awad
Keyword(s):  
Time Series ◽  
Walk Test ◽  
Minimal Set ◽  
Post Stroke ◽  
Point Estimates ◽  
Direct Measurements ◽  
Subject Specific ◽  
6 Minute Walk Test ◽  
Minute Walk ◽  
Anterior Posterior

Abstract Background: The anterior-posterior ground reaction force (AP-GRF) and propulsion and braking metrics derived from the AP-GRF time series are indicators of locomotor function across healthy and neurological diagnostic groups. In this paper, we describe the use of a minimal set of wearable inertial measurement units (IMUs) to indirectly measure the AP-GRFs generated during healthy and hemiparetic walking. Methods: Ten healthy individuals and five individuals with chronic post-stroke hemiparesis completed a 6-minute walk test over a walking track instrumented with six forceplates while wearing three IMUs securely attached to the pelvis, thigh, and shank. Subject-specific models driven by IMU-measured thigh and shank angles and an estimate of body acceleration provided by the pelvis IMU were used to generate indirect estimates of the AP-GRF time series. Propulsion and braking point metrics (i.e., peaks, peak timings, and impulses) were extracted from the IMU-generated time series. Peaks and impulses were expressed as % bodyweight (%bw) and peak timing was expressed as % stance phase (%sp). A 75%-25% split of 6-minute walk test data was used to train and validate the models. Indirect estimates of the AP-GRF time series and point metrics were compared to direct measurements of the same made by the reference standard forceplates. Results: Indirect measurements of the AP-GRF time series strongly approximated the direct measurements made by forceplates, with low error and high consistency in both the healthy (RMSE = 4.5 %bw; R2 = 0.93) and post-stroke (RMSE = 2.65 %bw; R2 = 0.90) cohorts. In the healthy cohort, the average errors between indirect and direct measurements of the peak propulsion magnitude, peak propulsion timing, and propulsion impulse point estimates were 2.37 %bw, 0.67 %sp, and 0.43 %bw. In the post-stroke cohort, the average errors for these same point estimates were 1.07 %bw, 1.27 %sp, and 0.31 %bw. Average errors for the braking-related point estimates were higher, but comparable. Conclusions: Accurate estimates of the AP-GRF time series and key propulsion and braking point metrics can be generated using three strategically mounted IMUs and subject-specific calibrations. This study is a foundational step toward the development of point-of-care diagnostic systems that can catalyze the routine assessment and management of propulsion and braking locomotor deficits during rehabilitation.

scholarly journals Estimation of grassland use intensities based on high spatial resolution LAI time series

2015 ◽  
Vol XL-7/W3 ◽  
pp. 285-291 ◽  
Author(s):  
S. Asam ◽  
D. Klein ◽  
S. Dech
Keyword(s):  
Time Series ◽  
Spatial Resolution ◽  
Management Practices ◽  
High Spatial Resolution ◽  
Vegetation Period ◽  
Grassland Management ◽  
Transfer Model ◽  
Land Use Patterns ◽  
Area Index ◽  
Intensively Managed

The identification and surveillance of agricultural management and the measurement of biophysical canopy parameters in grasslands is relevant for environmental protection as well as for political and economic reasons, as proper grassland management is partly subsidized. An ideal monitoring tool is remote sensing due to its area wide continuous observations. However, due to small-scaled land use patterns in many parts of central Europe, a high spatial resolution is needed. In this study, the feasibility of RapidEye data to derive leaf area index (LAI) time series and to relate them to grassland management practices is assessed. The study area is the catchment of river Ammer in southern Bavaria, where agricultural areas are mainly grasslands. While extensively managed grasslands are maintained with one to two harvests per year and no or little fertilization, intensive cultivation practices compass three to five harvests per year and turnover pasturing. <br><br> Based on a RapidEye time series from 2011 with spatial resolution of 6.5 meters, LAI is derived using the inverted radiation transfer model PROSAIL. The LAI in this area ranges from 1.5 to 7.5 over the vegetation period and is estimated with an RMSE between 0.7 and 1.1. The derived LAI maps cover 85 % of the study area’s grasslands at least seven times. Using statistical metrics of the LAI time series, different grassland management types can be identified: very intensively managed meadows, intensively managed meadows, intensively managed pastures, and extensively managed meadows and moor. However, a precise identification of the mowing dates highly depends on the coincidence with satellite data acquisitions. Further analysis should focus therefor on the selection of the temporal resolution of the time series as well as on the performance of further vegetation parameters and indices compared to LAI.

scholarly journals Trends of solar ultraviolet irradiance at Barrow, Alaska, and the effect of measurement uncertainties on trend detection

2011 ◽  
Vol 11 (9) ◽  
pp. 26617-26655 ◽  
Author(s):  
G. Bernhard
Keyword(s):  
Time Series ◽  
Systematic Errors ◽  
Correction Method ◽  
Natural Variability ◽  
Trend Detection ◽  
Transfer Model ◽  
Error Sources ◽  
Model Calculations ◽  
Uv Index ◽  
Measurement Uncertainties

Abstract. 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.

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