CAPENORTHPSEUDO_GEO4M_WGS84.TIF: 4-m Image of the Northern Half of the Pseudo-colored Backscatter Intensity of the Sea Floor off Northeastern Cape Cod (Geographic)

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.本数据集包含美国马萨诸塞州科德角东北近海海底的伪彩色（pseudo-colored）后向散射强度数据。该数据采集于1998年11月9日至25日开展的美国地质调查局（United States Geological Survey，USGS）98015号勘测任务，采用多波束海底测绘系统（multibeam sea floor mapping system）完成数据采集。本次勘测搭载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，使用Simrad EM 1000型多波束测深仪（multibeam echo sounder）进行作业。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度，可声呐覆盖最大达水深7.5倍的海底条带（本次勘测区域内条带宽度为100至200米）。海底波束的水平分辨率（horizontal resolution）约为水深的10%，垂直分辨率（vertical resolution）约为水深的1%。 伪彩色（pseudo-colored）后向散射强度将后向散射强度与海底地形（topography）相结合，用以展示强度分布与地形的对应关系。在本次展示的图像中，后向散射强度以8种色系组合表征，从代表低强度的蓝色到代表高强度的红色依次渐变。本数据集已叠加于经人工处理的晕渲地形图像（shaded relief image）之上：该图像将地形垂直夸张4倍，并以方位角（azimuth）0度、地平线以上45度的虚拟光源进行人工光照渲染。最终生成的图像中，每个色带（color band）内的明暗强度差异由地物相对于虚拟光源的位置决定。例如，北朝向坡面因接收充足光照，在色带中呈现高亮强度；而南朝向坡面处于阴影中，在色带中呈现低暗强度。