On the influence of wind and waves on the underwater light field

Abstract. We present a detailed study of the influence of various wind and wave conditions on the distribution of downwelling irradiance within the upper ocean mixed layer down to 100 m water depth. The work is based on a two-dimensional Monte Carlo radiative transfer model with high spatial resolution. We treat conditions that are favorable for the development of extreme light fluctuations, e.g. light at 490 nm and very clear oceanic water. Local wind determines the steepness of capillary-gravity waves which in turn dominate the irradiance variability near the surface. Maximum irradiance peaks that exceed the mean irradiance by a factor of more than 10 can be observed at low wind speeds up to 5 m s−1. Sea states influence the light field much deeper; gravity waves can cause considerable irradiance variability even at 100 m depth. The simulation results show that under realistic conditions 50 % radiative enhancements compared to the mean can still occur at 30 m depth.

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On the influence of wind and waves on underwater irradiance fluctuations

Ocean Science ◽

10.5194/os-8-455-2012 ◽

2012 ◽

Vol 8 (4) ◽

pp. 455-471 ◽

Cited By ~ 17

Author(s):

M. Hieronymi ◽

A. Macke

Keyword(s):

Gravity Waves ◽

Radiative Transfer Model ◽

Transfer Model ◽

Sea State ◽

Wind Speeds ◽

Light Fluctuations ◽

Underwater Irradiance ◽

The Mean ◽

Simulation Results ◽

Low Wind Speeds

Abstract. The influence of various wind and wave conditions on the variability of downwelling irradiance Ed (490 nm) in water is subject of this study. The work is based on a two-dimensional Monte Carlo radiative transfer model with high spatial resolution. The model assumes conditions that are ideal for wave focusing, thus simulation results reveal the upper limit for light fluctuations. Local wind primarily determines the steepness of capillary-gravity waves which in turn dominate the irradiance variability near the surface. Down to 3 m depth, maximum irradiance peaks that exceed the mean irradiance Ed by a factor of more than 7 can be observed at low wind speeds up to 5 m s−1. The strength of irradiance fluctuations can be even amplified under the influence of higher ultra-gravity waves; thereby peaks can exceed 11 Ed. Sea states influence the light field much deeper; gravity waves can cause considerable irradiance variability even at 100 m depth. The simulation results show that under realistic conditions 50% radiative enhancements compared to the mean can still occur at 30 m depth. At greater depths, the underwater light variability depends on the wave steepness of the characteristic wave of a sea state; steeper waves cause stronger light fluctuations.

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Modeling of wave-induced irradiance variability in the upper ocean mixed layer

Ocean Science Discussions ◽

10.5194/osd-8-2101-2011 ◽

2011 ◽

Vol 8 (5) ◽

pp. 2101-2146

Author(s):

M. Hieronymi ◽

A. Macke ◽

O. Zielinski

Keyword(s):

Radiative Transfer ◽

Monochromatic Light ◽

Radiative Transfer Model ◽

Transfer Model ◽

Underwater Light Field ◽

Irregular Wave ◽

The Mean ◽

Favorable Conditions ◽

Wave Induced ◽

Chlorophyll A Content

Abstract. A Monte Carlo based radiative transfer model has been developed for calculating the availability of solar radiation within the top 100 m of the ocean. The model is optimized for simulations of spatial high resolution downwelling irradiance Ed fluctuations that arise from the lensing effect of waves at the water surface. In a first step the accuracy of simulation results have been verified by measurements of the oceanic underwater light field and through intercomparison with an established radiative transfer model. Secondly the potential depth-impact of nonlinear shaped single waves, from capillary to swell waves, is assessed by considering the most favorable conditions for light focusing, i.e. monochromatic light at 490 nm, very clear oceanic water with a low chlorophyll a content of 0.1 mg m−3 and high sun elevation. Finally light fields below irregular wave profiles accounting for realistic sea states were simulated. Our simulations suggest that under open ocean conditions light flashes with 50 % irradiance enhancements can appear down to 35 m depth, and light variability in the range of ±10 % compared to the mean Ed is still possible in 100 m depth.

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Rapid coral mortality following unusually calm and hot conditions on Iriomote, Japan

F1000Research ◽

10.12688/f1000research.12660.2 ◽

2018 ◽

Vol 6 ◽

pp. 1728 ◽

Cited By ~ 2

Author(s):

Andrew H Baird ◽

Sally A. Keith ◽

Erika Woolsey ◽

Ryuta Yoshida ◽

Tohru Naruse

Keyword(s):

Water Movement ◽

Sea Surface ◽

Bleaching Event ◽

Coral Mortality ◽

Average Wind Speed ◽

Common Cause ◽

Wind Speeds ◽

Average Wind ◽

The Mean ◽

Low Wind Speeds

Coral bleaching can be induced by many different stressors, however, the most common cause of mass bleaching in the field is higher than average sea surface temperatures (SST). Here, we describe an unusual bleaching event that followed very calm sea conditions combined with higher than average SST. Patterns of mortality differed from typical bleaching in four ways: 1) mortality was very rapid; 2) a different suite of species were most affected; 3) tissue mortality in Acropora spp. was often restricted to the center of the colony; 4) the event occurred early in summer. The two weeks prior to the event included 8 days where the average wind speed was less than 3 ms-1. In addition, SSTs in the weeks preceding and during the event were 1.0-1.5°C higher than the mean for the last 30 years. We hypothesize that this unusual bleaching event was caused by anoxia resulting from a lack of water movement induced by low wind speeds combined with high SST.

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MINERAL ABUNDANCE AND PARTICLE SIZE DISTRIBUTION DERIVED FROM IN-SITU SPECTRA MEASUREMENTS OF YUTU ROVER OF CHANG’E-3

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-archives-xlii-3-w1-85-2017 ◽

2017 ◽

Vol XLII-3/W1 ◽

pp. 85-89

Author(s):

H. Lin ◽

X. Zhang ◽

Y. Yang ◽

X. Wu ◽

D. Guo

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Landing Site ◽

Radiative Transfer Model ◽

Transfer Model ◽

Particle Sizes ◽

The Mean ◽

The Difference ◽

Yutu Rover

From geologic perspective, understanding the types, abundance, and size distributions of minerals allows us to address what geologic processes have been active on the lunar and planetary surface. The imaging spectrometer which was carried by the Yutu Rover of Chinese Chang’E-3 mission collected the reflectance at four different sites at the height of ~&thinsp;1&thinsp;m, providing a new insight to understand the lunar surface. The mineral composition and Particle Size Distribution (PSD) of these four sites were derived in this study using a Radiative Transfer Model (RTM) and Sparse Unmixing (SU) algorithm. The endmembers used were clinopyroxene, orthopyroxene, olivine, plagioclase and agglutinate collected from the lunar sample spectral dataset in RELAB. The results show that the agglutinate, clinopyroxene and olivine are the dominant minerals around the landing site. In location Node E, the abundance of agglutinate can reach up to 70&thinsp;%, and the abundances of clinopyroxene and olivine are around 10&thinsp;%. The mean particle sizes and the deviations of these endmembers were retrieved. PSDs of all these endmembers are close to normal distribution, and differences exist in the mean particle sizes, indicating the difference of space weathering rate of these endmembers.

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Influence of spatial heterogeneity of local surface albedo on the area-averaged surface albedo retrieved from airborne irradiance measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-6-527-2013 ◽

2013 ◽

Vol 6 (3) ◽

pp. 527-537 ◽

Cited By ~ 9

Author(s):

E. Jäkel ◽

M. Wendisch ◽

B. Mayer

Keyword(s):

Optical Depth ◽

Surface Albedo ◽

Radiative Transfer Model ◽

Small Scale ◽

Mean Deviation ◽

Transfer Model ◽

Horizontal Distance ◽

Local Surface ◽

Atmospheric Scattering ◽

The Mean

Abstract. Spectral airborne upward and downward irradiance measurements are used to derive the area-averaged surface albedo. Real surfaces are not homogeneous in their reflectivity. Therefore, this work studies the effects of the heterogeneity of surface reflectivity on the area-averaged surface albedo to quantify how well aircraft measurements can resolve the small-scale variability of the local surface albedo. For that purpose spatially heterogeneous surface albedo maps were input into a 3-dimensional (3-D) Monte Carlo radiative transfer model to simulate 3-D irradiance fields. The calculated up- and downward irradiances in altitudes between 0.1 and 5 km are used to derive the area-averaged surface albedo using an iterative retrieval method that removes the effects due to atmospheric scattering and absorption within the layer beneath the considered level. For the case of adjacent land and sea surfaces, parametrizations are presented which quantify the horizontal distance from the coastline that is required to reduce surface heterogeneity effects on the area-averaged surface albedo to a given limit. The parametrization which is a function of altitude, aerosol optical depth, single scattering albedo, and the ratio of local land and sea albedo was applied for airborne spectral measurements. In addition, the deviation between area-averaged and local surface albedo is determined for more complex surface albedo maps. For moderate aerosol conditions (optical depth less than 0.4) and a wavelength range between 400 and 1000 nm, the altitude and the heterogeneity of the surface albedo are the dominant factors determining the mean deviation between local and area-averaged surface albedo. A parametrization of the mean deviation is applied to an albedo map that was derived from a Landsat image of an area in East Anglia (UK). Parametrization and direct comparison of local and area-averaged surface albedo show similar mean deviations (20% vs. 25%) over land.

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High resolution and Monte Carlo additions to the SASKTRAN radiative transfer model

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-3357-2015 ◽

2015 ◽

Vol 8 (3) ◽

pp. 3357-3397 ◽

Cited By ~ 1

Author(s):

D. J. Zawada ◽

S. R. Dueck ◽

L. A. Rieger ◽

A. E. Bourassa ◽

N. D. Lloyd ◽

...

Keyword(s):

Monte Carlo ◽

High Resolution ◽

Radiative Transfer ◽

Spatial Resolution ◽

High Spatial Resolution ◽

Reference Model ◽

Monte Carlo Model ◽

Radiative Transfer Model ◽

Transfer Model ◽

Systematic Bias

Abstract. The OSIRIS instrument on board the Odin spacecraft has been measuring limb scattered radiance since 2001. The vertical radiance profiles measured as the instrument nods are inverted, with the aid of the SASKTRAN radiative transfer model, to obtain vertical profiles of trace atmospheric constituents. Here we describe two newly developed modes of the SASKTRAN radiative transfer model: a high spatial resolution mode, and a Monte Carlo mode. The high spatial resolution mode is a successive orders model capable of modelling the multiply scattered radiance when the atmosphere is not spherically symmetric; the Monte Carlo mode is intended for use as a highly accurate reference model. It is shown that the two models agree in a wide variety of solar conditions to within 0.2%. As an example case for both models, Odin-OSIRIS scans were simulated with the Monte Carlo model and retrieved using the high resolution model. A systematic bias of up to 4% in retrieved ozone number density between scans where the instrument is scanning up or scanning down was identified. It was found that calculating the multiply scattered diffuse field at five discrete solar zenith angles is sufficient to eliminate the bias for typical Odin-OSIRIS geometries.

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Retrieving the characteristics of slab ice covering snow by remote sensing

The Cryosphere ◽

10.5194/tc-10-2113-2016 ◽

2016 ◽

Vol 10 (5) ◽

pp. 2113-2128 ◽

Cited By ~ 3

Author(s):

François Andrieu ◽

Frédéric Schmidt ◽

Bernard Schmitt ◽

Sylvain Douté ◽

Olivier Brissaud

Keyword(s):

Thick Layer ◽

Radiative Transfer Model ◽

Inversion Method ◽

Transfer Model ◽

Retrieval Method ◽

Water Ice ◽

Air Interface ◽

The Mean ◽

Experimental Validations ◽

Grain Diameter

Abstract. We present an effort to validate a previously developed radiative transfer model, and an innovative Bayesian inversion method designed to retrieve the properties of slab-ice-covered surfaces. This retrieval method is adapted to satellite data, and is able to provide uncertainties on the results of the inversions. We focused on surfaces composed of a pure slab of water ice covering an optically thick layer of snow in this study. We sought to retrieve the roughness of the ice–air interface, the thickness of the slab layer and the mean grain diameter of the underlying snow. Numerical validations have been conducted on the method, and showed that if the thickness of the slab layer is above 5 mm and the noise on the signal is above 3 %, then it is not possible to invert the grain diameter of the snow. In contrast, the roughness and the thickness of the slab can be determined, even with high levels of noise up to 20 %. Experimental validations have been conducted on spectra collected from laboratory samples of water ice on snow using a spectro-radiogoniometer. The results are in agreement with the numerical validations, and show that a grain diameter can be correctly retrieved for low slab thicknesses, but not for bigger ones, and that the roughness and thickness are correctly inverted in every case.

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Dynamic Response of Articulated Tower Platforms to Random Sea Environment

Volume 1: Offshore Technology ◽

10.1115/omae2009-79357 ◽

2009 ◽

Author(s):

Mohd Moonis Zaheer ◽

Nazrul Islam

Keyword(s):

Dynamic Response ◽

Excitation Frequency ◽

Response Analysis ◽

Wave Forces ◽

Wind Gust ◽

Wave Age ◽

Wind Speeds ◽

Positive Side ◽

The Mean ◽

Low Wind Speeds

Articulated tower motions have been characterized by rigid body mode of vibrations falling in the wind excitation frequency range due to its compliant nature. Dynamic response analysis of a multi hinged articulated tower platform to random wind and wave forces are presented in this paper. The wave forces on the submerged elements of the tower are calculated by using Morison’s Equation. The fluctuating wind is modeled with Ochi and Shin wind gust spectrum. The effect of wave age (young, intermediate and fully developed waves) on the wind gust spectrum is incorporated by adopting the wave age dependent Volkov, and wave age independent Charnock sea surface roughness models. The response of the tower is determined by a time domain iterative method. An example of results demonstrates the clear effect of wave age on the nonlinear dynamic response on the system. The mean wind modifies the mean position of the surge response to the positive side, causing an offset. Moreover, for high mean wind speeds the total wind response is much smaller than the wave response, but for low wind speeds the wind appears to be more important.

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Influence of spatial heterogeneity of local surface albedo on the area-averaged surface albedo retrieved from airborne irradiance measurements

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-5-7457-2012 ◽

2012 ◽

Vol 5 (5) ◽

pp. 7457-7487

Author(s):

E. Jäkel ◽

M. Wendisch ◽

B. Mayer

Keyword(s):

Optical Depth ◽

Surface Albedo ◽

Radiative Transfer Model ◽

Small Scale ◽

Mean Deviation ◽

Transfer Model ◽

Horizontal Distance ◽

Local Surface ◽

Atmospheric Scattering ◽

The Mean

Abstract. Spectral airborne upward and downward irradiance measurements are used to derive the area-averaged surface albedo. Real surfaces are not homogeneous in their reflectivity. Therefore, this work studies the effects of the heterogeneity of surface reflectivity on the area-averaged surface albedo to quantify how well aircraft measurements can resolve the small-scale variability of the local surface albedo. For that purpose spatially heterogeneous surface albedo maps were input into a 3-dimensional (3-D) Monte Carlo radiative transfer model to simulate 3-D irradiance fields. The calculated up- and downward irradiances in altitudes between 0.1 km and 5 km are used to derive the area-averaged surface albedo using an iterative retrieval method that removes the effects due to atmospheric scattering and absorption within the layer beneath the considered level. For the case of adjacent land and sea surfaces a parametrization is presented which quantifies the horizontal distance to the coastline that is required to reduce surface heterogeneity effects on the area-averaged surface albedo to a given limit. The parametrization which is a function of altitude, aerosol optical depth, and the ratio of local land and sea albedo was applied for airborne spectral measurements. In addition, the deviation between area-averaged and local surface albedo is determined for more complex surface albedo maps. For moderate aerosol conditions (optical depth less than 0.4) and the visible wavelength range, the altitude and the heterogeneity of the surface albedo are the dominant factors determining the mean deviation between local and area-averaged surface albedo. A parametrization of the mean deviation is applied to an albedo map that was derived from a Landsat image of an area in East Anglia (UK). Parametrization and direct comparison of local and area-averaged surface albedo show similar mean deviations (20% vs. 25%) over land.

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Comparison of regional chemistry-modelled NO2 tropospheric columns and profiles with TROPOMI observations and 4-azimuth MAX-DOAS measurements

10.5194/egusphere-egu2020-1934 ◽

2020 ◽

Author(s):

Vinod Kumar ◽

Julia Remmers ◽

Benedikt Steil ◽

Astrid Kerkweg ◽

Jos Lelieveld ◽

...

Keyword(s):

Spatial Resolution ◽

High Spatial Resolution ◽

Climate Modeling ◽

Temporal Correlation ◽

Domain Model ◽

Trace Gas ◽

Radiative Transfer Model ◽

Transfer Model ◽

Regional Models ◽

Vertical Column

Regional chemistry-transport models typically simulate the physical and chemical state of the atmosphere at a high spatial resolution, e.g. of less than 7 km. At this relatively high spatial resolution, air quality and relevant processes within cities can be assessed to facilitate strategic mitigation planning. Comparison of regional models with satellite and ground-based observations helps validate the models and evaluate emission inventories, as well as satellite retrieval algorithms. For example, an underestimation of atmospheric trace gases (like often found for NO2) by satellite observations can be improved by providing high-resolution input fields from regional models.MECO(n), a global-to-regional chemistry climate modeling system, in which the finer resolved domains receive their initial and boundary conditions on-line from the next coarser model instance, was set-up with Germany as focus. 1-way nested MECO(3)&#160; simulations were performed for May 2018 with spatial resolution up to ~2.2 km &#215; 2.2 km in the finest domain. Model simulations accounting separately for both TNO MACC III and EDGAR 4.3.2 anthropogenic emissions are evaluated against TROPOMI observations. A diurnal factor was applied to road transport emissions to account for their temporal variation. For the comparison with TROPOMI data, we applied a novel method of online sampling of model fields along the satellite overpass by also accounting for the difference in local solar time across the swath width, which can be up to 90 minutes. Modified airmass factors in the TROPOMI data product, using the model calculated NO2 a priori profiles and taking into account averaging kernels, resulted in an improved agreement of the spatial pattern of NO2 vertical column density (VCD) between model and satellite.NO2 VCDs over Mainz, calculated using model output at the finest model resolution, were compared against MAX-DOAS observations for the simulation period. Vertical profiles of NO2 were also retrieved in 4 azimuth directions around Mainz by profile inversion of MAX-DOAS measurements. The temporal (e.g. day-to-day and diurnal) variation of the 3-D NO2 field derived from the model was evaluated against the MAX-DOAS observations. For the cloud-free days, the model is able to reproduce the temporal development with satisfactory temporal correlation (slope=0.7, r=0.5) of the NO2 VCDs. For a direct comparison of measured slant column densities of NO2, height-resolved 2-D box airmass factors were calculated using McArtim (Monte Carlo Atmospheric radiative transfer model) and applied to the modelled trace gas profiles along individual elevation angles of the measurements. This comparison procedure accounts for the complex dependency of the MAX-DOAS column densities on the 3D (vertical and horizontal) trace gas distribution in the measurement direction.

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