4-m Image of the Southern Half of the Pseudo-colored Backscatter Intensity of the Sea Floor off Eastern Cape Cod (CAPESOUTHPSEUDO_GEO4M_WGS84.TIF, Geographic, WGS84)

This data set includes pseudo-colored backscatter intensity of the sea floor offshore of northeastern Cape Cod, Massachusetts. The data were collected with a multibeam sea floor mapping system during USGS survey 98015, conducted November 9 - 25, 1998. The surveys were conducted using a Simrad EM 1000 multibeam echo sounder mounted aboard the Canadian Coast Guard vessel Frederick G. Creed. This multibeam system utilizes 60 electronically aimed receive beams spaced at intervals of 2.5 degrees that insonify a strip of sea floor up to 7.5 times the water depth (swath width of 100 to 200 m within the survey area). The horizontal resolution of the beam on the sea floor is approximately 10% of the water depth. Vertical resolution is approximately 1 percent of the water depth. With pseudo-colored backscatter intensity, the backscatter intensity is combined with the topography to display the distribution of intensity in relation to the topography. In the image shown here, the backscatter intensity is represented by a suite of eight colors ranging from blue, which represents low intensity, to red, which represents high intensity. These data are draped over a shaded relief image created by vertically exaggerating the topography four times and then artificially illuminating the relief by a light source positioned 45 degrees above the horizon from an azimuth of 0 degrees. The resulting image displays light and dark intensities within each color band that result from a feature's position with respect to the light source. For example, north-facing slopes, receiving strong illumination, show as a light intensity within a color band, whereas south-facing slopes, being in shadow, show as a dark intensity within a color band.本数据集涵盖美国马萨诸塞州科德角东北部近海海底的伪彩色后向散射强度（pseudo-colored backscatter intensity）数据。该数据采集于1998年11月9日至25日实施的美国地质调查局（United States Geological Survey, USGS）98015号科考航次，由多波束海底测绘系统（multibeam sea floor mapping system）完成数据采集。本次航次搭载了安装于加拿大海岸警卫队“弗雷德里克·G·克里德”号（Frederick G. Creed）科考船上的Simrad EM 1000多波束回声测深仪（multibeam echo sounder）。该多波束系统配备60个电子定向接收波束，波束间距为2.5°，可声扫覆盖最大达7.5倍水深的海底条带（本次航次覆盖条带宽度为100~200米）。海底波束的水平分辨率约为水深的10%，垂直分辨率约为水深的1%。 在伪彩色后向散射强度可视化流程中，后向散射强度与海底地形相融合，用以展示强度随地形的分布特征。本示例图像中，后向散射强度由8种颜色序列表征，从代表低强度的蓝色渐变至代表高强度的红色。该数据叠加于一幅晕渲地貌图（shaded relief image）：该图先将地形起伏放大4倍，再通过方位角0°、地平线以上45°的人工光源对地貌进行人工光照，生成晕渲效果。最终生成的图像中，同一色带内存在明暗差异，该差异由地貌特征相对于光源的位置所决定。例如，北坡受光照充足，在色带中呈现高亮强度；南坡处于阴影之中，在色带中呈现低暗强度。