scholarly journals Atmospheric Fronts along the East Coast of Taiwan Studied by ERS Synthetic Aperture Radar Images

2007 ◽  
Vol 64 (3) ◽  
pp. 922-937 ◽  
Author(s):  
Werner Alpers ◽  
Jen-Ping Chen ◽  
I-I. Lin ◽  
Chun-Chi Lien
Keyword(s):  
Synthetic Aperture Radar ◽  
East Coast ◽  
Sea Surface ◽  
Offshore Wind ◽  
Synthetic Aperture ◽  
Katabatic Wind ◽  
Land Breeze ◽  
Mountain Range ◽  
Synoptic Scale ◽  
Atmospheric Fronts

Abstract The existence of quasi-stationary alongshore atmospheric fronts typically located 30–70 km off the east coast of Taiwan is demonstrated by analyzing synthetic aperture radar (SAR) images of the sea surface acquired by the European Remote Sensing Satellites ERS-1 and ERS-2. For the data interpretation, cloud images from the Japanese Geostationary Meteorological Satellite GMS-4 and the American Terra satellite, rain-rate maps from ground-based weather radars, sea surface wind data from the scatterometer on board the Quick Scatterometer (QuikSCAT) satellite, and meteorological data from weather maps and radiosonde ascents have also been used. It is shown that these atmospheric fronts are generated by the collisions of the two airflows from opposing directions: one is associated with a weak easterly synoptic-scale wind blowing against the high coastal mountain range at the east coast of Taiwan and the other with a local offshore wind. At the convergence zone where both airflows collide, air is forced to move upward, which often gives rise to the formation of coast-parallel cloud bands. There are two hypotheses about the origin of the offshore wind. The first one is that it is a thermally driven land breeze/katabatic wind, and the second one is that it is wind resulting from recirculated airflow from the synoptic-scale onshore wind. Air blocked by the mountain range at low Froude numbers is recirculated and flows at low levels back offshore. Arguments in favor of and against the two hypotheses are presented. It is argued that both the recirculation of airflow and land breeze/katabatic wind contribute to the formation of the offshore atmospheric front but that land breeze/katabatic wind is probably the main cause.

scholarly journals On the Origin of Atmospheric Frontal Lines off the East Coast of Taiwan Observed on Spaceborne Synthetic Aperture Radar Images

2010 ◽  
Vol 138 (2) ◽  
pp. 475-496 ◽  
Author(s):  
Werner Alpers ◽  
Jen-Ping Chen ◽  
Chia-Jung Pi ◽  
I-I. Lin
Keyword(s):  
Synthetic Aperture Radar ◽  
East Coast ◽  
Physical Mechanism ◽  
Mesoscale Model ◽  
Synthetic Aperture ◽  
Katabatic Wind ◽  
Mountain Range ◽  
Sar Images ◽  
Radar Images ◽  
Aperture Radar

Abstract Frontal lines having offshore distances typically between 40 and 80 km are often visible on synthetic aperture radar (SAR) images acquired over the east coast of Taiwan by the European Remote Sensing Satellites 1 and 2 (ERS-1 and ERS-2) and Envisat. In a previous paper the authors showed that they are of atmospheric and not of oceanic origin; however, in that paper they did not give a definite answer to the question of which physical mechanism causes them. In this paper the authors present simulations carried out with the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model, which shows that the frontal lines are associated with a quasi-stationary low-level convergence zone generated by the dynamic interaction of onshore airflow of the synoptic-scale wind with the coastal mountain range of the island of Taiwan. Reversed airflow collides with the onshore-flowing air leading to an uplift of air, which is often accompanied by the formation of bands of increased cloud density and of rainbands. The physical mechanism causing the generation of the frontal lines is similar to the one responsible for the formation of cloud bands off the Island of Hawaii as described by Smolarkiewicz et al. Four SAR images are shown, one acquired by ERS-2 and three by Envisat, showing frontal lines at the east coast of Taiwan caused by this generation mechanism. For these events the recirculation pattern, as well as the frontal (or convective) lines observed, were reproduced quite well with the meteorological model. So, it is argued that the observed frontal lines are not seaward boundaries of (classical) barrier jets or of katabatic wind fields, which have characteristics that are quite different from the flow patterns around the east coast of Taiwan as indicated by the SAR images.

scholarly journals Use of Synthetic Aperture Radar in Finescale Surface Analysis of Synoptic-Scale Fronts at Sea

2005 ◽  
Vol 20 (3) ◽  
pp. 311-327 ◽  
Author(s):  
G. S. Young ◽  
T. N. Sikora ◽  
N. S. Winstead
Keyword(s):  
North America ◽  
Synthetic Aperture Radar ◽  
East Coast ◽  
Gulf Of Alaska ◽  
Data Sources ◽  
Synthetic Aperture ◽  
Synoptic Scale ◽  
Sar Images ◽  
Cold Fronts ◽  
Aperture Radar

Abstract The viability of synthetic aperture radar (SAR) as a tool for finescale marine meteorological surface analyses of synoptic-scale fronts is demonstrated. In particular, it is shown that SAR can reveal the presence of, and the mesoscale and microscale substructures associated with, synoptic-scale cold fronts, warm fronts, occluded fronts, and secluded fronts. The basis for these findings is the analysis of some 6000 RADARSAT-1 SAR images from the Gulf of Alaska and from off the east coast of North America. This analysis yielded 158 cases of well-defined frontal signatures: 22 warm fronts, 37 cold fronts, 3 stationary fronts, 32 occluded fronts, and 64 secluded fronts. The potential synergies between SAR and a range of other data sources are discussed for representative fronts of each type.

scholarly journals US East Coast synthetic aperture radar wind atlas for offshore wind energy

2020 ◽  
Vol 5 (3) ◽  
pp. 1191-1210 ◽  
Author(s):  
Tobias Ahsbahs ◽  
Galen Maclaurin ◽  
Caroline Draxl ◽  
Christopher R. Jackson ◽  
Frank Monaldo ◽  
...  
Keyword(s):  
Wind Speed ◽  
Synthetic Aperture Radar ◽  
East Coast ◽  
Offshore Wind ◽  
Synthetic Aperture ◽  
The Us ◽  
Wind Retrievals ◽  
Wind Resources ◽  
Us East Coast ◽  
Aperture Radar

Abstract. We present the first synthetic aperture radar (SAR) offshore wind atlas of the US East Coast from Georgia to the Canadian border. Images from RADARSAT-1, Envisat, and Sentinel-1A/B are processed to wind maps using the geophysical model function (GMF) CMOD5.N. Extensive comparisons with 6008 collocated buoy observations of the wind speed reveal that biases of the individual systems range from −0.8 to 0.6 m s−1. Unbiased wind retrievals are crucial for producing an accurate wind atlas, and intercalibration of the SAR observations is therefore applied. Wind retrievals from the intercalibrated SAR observations show biases in the range of to −0.2 to 0.0 m s−1, while at the same time improving the root-mean-squared error from 1.67 to 1.46 m s−1. The intercalibrated SAR observations are, for the first time, aggregated to create a wind atlas at the height 10 m a.s.l. (above sea level). The SAR wind atlas is used as a reference to study wind resources derived from the Wind Integration National Dataset Toolkit (WTK), which is based on 7 years of modelling output from the Weather Research and Forecasting (WRF) model. Comparisons focus on the spatial variation in wind resources and show that model outputs lead to lower coastal wind speed gradients than those derived from SAR. Areas designated for offshore wind development by the Bureau of Ocean Energy Management are investigated in more detail; the wind resources in terms of the mean wind speed show spatial variations within each designated area between 0.3 and 0.5 m s−1 for SAR and less than 0.2 m s−1 for the WTK. Our findings indicate that wind speed gradients and variations might be underestimated in mesoscale model outputs along the US East Coast.

scholarly journals US East Coast synthetic aperture radar wind atlas for offshore wind energy

2019 ◽  
Author(s):  
Tobias Ahsbahs ◽  
Galen Maclaurin ◽  
Caroline Draxl ◽  
Christopher Jackson ◽  
Frank Monaldo ◽  
...  
Keyword(s):  
Wind Speed ◽  
Synthetic Aperture Radar ◽  
East Coast ◽  
Mesoscale Model ◽  
Wrf Model ◽  
Offshore Wind ◽  
Synthetic Aperture ◽  
Wind Resources ◽  
Us East Coast ◽  
Aperture Radar

Abstract. We present the first synthetic aperture radar (SAR)-based offshore wind atlas of the US East Coast from Georgia to the Canadian border. Images from Radarsat-1, Envisat, Sentinel-1A, and Sentinel-1B are processed to wind maps using the Geophysical Model Function (GMF) CMOD5.N. Extensive comparisons with 6,008 collocated buoy observations revealed that biases of the individual system range from −0.8 to 0.6 m/s. Unbiased wind retrievals are crucial for producing an accurate wind atlas and intercalibration for correcting these biases by adjusting the normalized radar cross section is applied. The intercalibrated SAR observations show biases in the range of to −0.2 to 0.0 m/s, while at the same time improving the root mean squared error from 1.67 to 1.46 m/s. These intercalibrated SAR observations are, for the first time, aggregated to create a wind atlas. Monthly averages are used to correct artefacts from seasonal biases. The SAR wind atlas is used as a reference to study wind resources derived from the Weather Research and Forecasting (WRF) model. Comparisons focus on the spatial variation of wind resources and show that model results estimate lower coastal wind speed gradients than those from SAR. At sites designated for offshore wind development by the Bureau of Ocean Energy Management, mean wind speeds typically vary between 0.3 and 0.5 m/s for SAR and less than 0.2 m/s for the WRF model within each site. Findings indicate that wind speed gradients and variation might be underestimated in mesoscale model outputs along US East Coast.

scholarly journals Exploring the coastal effects relevant for offshore wind farming using the space borne synthetic aperture radar data in the German Bight

2021 ◽  
Author(s):  
Bughsin Djath ◽  
Johannes Schulz-Stellenfleth
Keyword(s):  
Thermal Stability ◽  
Wind Speed ◽  
Synthetic Aperture Radar ◽  
German Bight ◽  
Atmospheric Stability ◽  
Sea Surface ◽  
Offshore Wind ◽  
Synthetic Aperture ◽  
Horizontal Wind ◽  
Wind Speeds

<p>In the coastal zone complex atmospheric processes such as momentum and heat fluxes are  caused by large differences between the land and the sea. The smoother sea surface leads to wind speeds, which are usually higher over the ocean than over land. In addition, there are complicated effects caused by temperature gradients in the ocean due to water depth variations.  This study focuses on the investigation of the change in the horizontal wind field and the atmospheric stability between the coast and up to 200 km offshore.</p><p>The wind resources at 10 m height are assessed from synthetic aperture radar (SAR) data acquired by the satellites Sentinel1A/B over the German Bight within the period of 2017-2020 with a focus on offshore wind directions. The satellite data provide information on sea surface roughness, which can be linked to near surface wind speed.  Information on the air-sea thermal components is  provided by model data from the German weather service (DWD).</p><p>The SAR data  show a significant increase of wind speed offshore in most cases. Increasing wind speeds between land and sea over fetch distances of 70 km and more are often detected. The increase δu in horizontal wind speed between offshore and the coast exceeds 2.5 m/s in average. Furthermore, the estimated atmospheric stability shows an impact on the wind speed gradients. The thermal stability appears to dictate the distance over which the wind increases. Strong thermal stability tends to influence the horizontal wind gradient by increasing the fetch distance over more than 100 km. In the context of offshore wind farming, the potential effects of these horizontal wind gradients on the wind power will be discussed.</p>

Effectiveness of WRF wind direction for retrieving coastal sea surface wind from synthetic aperture radar

Wind Energy ◽  
2012 ◽  
Vol 16 (6) ◽  
pp. 865-878 ◽  
Author(s):  
Yuko Takeyama ◽  
Teruo Ohsawa ◽  
Katsutoshi Kozai ◽  
Charlotte Bay Hasager ◽  
Merete Badger
Keyword(s):  
Synthetic Aperture Radar ◽  
Wind Direction ◽  
Surface Wind ◽  
Sea Surface ◽  
Synthetic Aperture ◽  
Sea Surface Wind ◽  
Coastal Sea ◽  
Aperture Radar

scholarly journals Marine Oil Spill Detection Based on the Comprehensive Use of Polarimetric SAR Data

2018 ◽  
Vol 10 (12) ◽  
pp. 4408 ◽  
Author(s):  
Yu Li ◽  
Yuanzhi Zhang ◽  
Zifeng Yuan ◽  
Huaqiu Guo ◽  
Hongyuan Pan ◽  
...  
Keyword(s):  
Synthetic Aperture Radar ◽  
Crude Oil ◽  
Oil Spill ◽  
Sea Surface ◽  
Synthetic Aperture ◽  
Polarimetric Sar ◽  
Classification Result ◽  
Marine Oil ◽  
Oil Spill Detection ◽  
Biogenic Slicks

As a major marine pollution source, oil spills largely threaten the sustainability of the coastal environment. Polarimetric synthetic aperture radar remote sensing has become a promising approach for marine oil spill detection since it could effectively separate crude oil and biogenic look-alikes. However, on the sea surface, the signal to noise ratio of Synthetic Aperture Radar (SAR) backscatter is usually low, especially for cross-polarized channels. In practice, it is necessary to combine the refined detail of slick-sea boundary derived from the co-polarized channel and the highly accurate crude slick/look-alike classification result obtained based on the polarimetric information. In this paper, the architecture for oil spill detection based on polarimetric SAR is proposed and analyzed. The performance of different polarimetric SAR filters for oil spill classification are compared. Polarimetric SAR features are extracted and taken as the input of Staked Auto Encoder (SAE) to achieve high accurate classification between crude oil, biogenic slicks, and clean sea surface. A post-processing method is proposed to combine the classification result derived from SAE and the refined boundary derived from VV channel power image based on special density thresholding (SDT). Experiments were conducted on spaceborne fully polarimetric SAR images where both crude oil and biogenic slicks were presented on the sea surface.

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