墨西哥湾浮油图片集编辑本段回目录
墨西哥湾浮油图片集：常见问题
撰文：瑞贝卡·林赛(Rebecca Lindsey)
设计：罗伯特·西蒙(Robert Simmon)
2010年7月21日
Twice-daily images of the Gulf of Mexico are available from the MODIS Rapid Response Team. The images in our Gulf Oil Spill gallery include annotation and interpretation.
每天两次的墨西哥湾图像由MODIS(译注1)快速反应小组提供。在我们的海湾原油泄漏图集中的图像都含有注解。
On April 20, 2010, a deadly explosion at the Deepwater Horizon offshore drilling platform started a catastrophic oil leak into the waters of the Gulf of Mexico. NASA’s imaging satellites captured pictures of the Gulf the next day, showing a plume of smoke spreading eastward from the still-smoldering rig.
2010年4月20日，发生在深水地平线海上钻井平台的剧烈爆炸，墨西哥湾水域的灾难性的原油泄漏拉开了帷幕。NASA(译注2)的成像卫星于翌日对海湾进行了拍摄，图像显示一大片烟雾以仍冒着烟的钻机为起点向东蔓延。
A NASA satellite saw smoke from the burning Deepwater Horizon oil rig on April 20, 2010. (NASA image courtesy MODIS Rapid Response Team.)
2010年4月20日，NASA的一颗卫星观测到从燃烧着的深水地平线石油钻井平台上飘起的烟雾。（NASA，MODIS快速反应小组供图.）
After several cloudy days, the first image showing significant oil on the surface was captured on the afternoon of April 25 by the Aqua satellite. By the time Aqua’s sister satellite, Terra, flew overhead the next morning, however, the oil was no longer visible—even though it was still there.
在经过数日多云天气后，阿卡(Aqua)卫星于4月25日下午拍摄到第一张显示在海洋表面上有大量的油污的图像。翌日上午，阿卡的姐妹星——泰拉(Terra)卫星从该地点上方飞过，尽管油污还是充斥原处，但却无法被观测到。
By April 25, 2010 (top), a spreading oil slick was visible off the coast of Louisiana. On the morning of the 26th (bottom), the slick appeared to disappear, but this was due to changes in lighting conditions, not the absence of oil. (NASA images courtesy MODIS Rapid Response Team.)
2010年4月25日（上图），可以观测到路易斯安那州海岸远处有浮油蔓延。在26日上午（下图），浮油似乎消失了，但是这只是由于光照条件的变化导致的，而不是油污真的消失了。（NASA，MODIS快速反应小组供图.）
That hit and miss pattern has repeated itself often in the four months the leak has continued, and we’ve put together this FAQ to explain why we don’t post new oil slick images every day.
自原油泄漏开始的四个月来，像那样碰运气的模式反复出现，于是我们归纳整理了这些常见问题，来解释为什么我们不是每天都上传浮油的最新图像。
Why don’t you post images every day?
NASA satellites don’t capture good images of the oil slick every day. NASA’s Terra and Aqua satellites are the only two missions whose pictures are available in near-real time, and they are the only two missions that capture pictures of almost every place on Earth every day.
为什么你们不是每天都上传图像？
NASA的卫星并不是每天都能拍摄到符合要求的浮油图像。NASA的泰拉和阿卡卫星是唯一的两颗能够提供近实时图像的任务卫星，同时它们也是唯一的两颗可以每天拍摄几乎地球上任一地点的任务卫星。
But unlike weather satellites that look at the same region on Earth 24 hours a day, Terra and Aqua generally only get one daylight view each of the Gulf of Mexico. Terra’s view is shortly before noon each day, and Aqua’s is shortly after. The view may be cloudy or hazy, and if the oil slick location is near the edge of the image, it will be blurry.
但与每天24小时盯着地球同一个区域的气象卫星不同，一般情况下泰拉和阿卡只能各获取一张有关墨西哥湾的白天视图。泰拉的视图大约是在每天中午前不久，而阿卡则是中午过后不久。视图可能阴沉而朦胧，如果浮油区域靠近图像边缘的话，则会显得模糊。
Clouds often obscure the oil slick in the humid Gulf (top, April 30), and sometimes the slick is near the edge of the satellites’ field of view (bottom, May 8). (NASA images courtesy MODIS Rapid Response Team.)
云层往往会掩盖潮湿的海湾上的浮油（上图，摄于4月30日），而有时浮油则靠近卫星的视场边缘（下图，摄于5月8日）。（NASA，MODIS快速反应小组供图.）
Even on a clear day, an oil slick may be imperceptible in photo-like satellite images. Like cooking oil added to a pot of water, a stream of crude oil disperses across the ocean surface into droplets and thin streamers. Against the already dark backdrop of the open ocean, the oil may not be detectable unless it is very thick or it is located in the part of the satellite image affected by sunglint.
即使是在天气晴朗的日子，浮油也可能会在照片级卫星图像中难以辨认。宛如在一锅水中倒入烹调油一样，原油带会在海洋表面分散成油滴和薄薄的油带。鉴于公海原本的深色背景，若非油污本身就非常厚或者恰巧位于卫星图像中受到日光返辉影响的区域，否则是很难发现油污踪迹的。
What is sunglint?
The sunglint area is a bright strip that runs roughly north-south through satellite pictures of the ocean. It is caused by the mirror-like reflection of the Sun off the water; in sunglint regions, the ocean surface is reflecting a lot of light back to the satellite at the same angle at which the light hit the ocean.
什么是日光返辉(sunglint)？
日光返辉带是一条明亮的地带，在卫星图片中大致横跨海洋的南北。它是由水面对于太阳的镜面反射引起的；在日光返辉地区，日光照射到海洋表面后反射回来的大量光线与卫星处于同一角度。
If the water were as smooth as a mirror, a line of perfect reflections of the Sun would appear in images such as this. Instead, small waves and ripples blur the reflection into a wide, bright strip—the sunglint region. This image was captured in 2009, before the Gulf oil leak. (NASA image courtesy MODIS Rapid Response Team.)
如果水面像镜子一样光滑，一束完美的太阳反射光便会在这样的图像中出现。否则，细浪和涟漪会将反射光模糊成一个宽广明亮的带状区域——即日光返辉区域。这张图像拍摄于2009年，海湾原油泄漏发生前。（NASA，MODIS快速反应小组供图.）
Most of the images of the oil slick that the Earth Observatory has published come from a sensor called MODIS, a copy of which flies on both the Terra and Aqua satellites. If the ocean were as smooth as a mirror, a sequence of nearly perfect reflections of the Sun, each with a width between 6-9 kilometers, would appear in the water in a line along the track of the satellite’s orbit.
大多数地球大观发布的有关浮油的图像是来自同时搭载于泰拉和阿卡卫星上的，叫做MODIS的传感器的数据的副本。如果海面像镜子一样平滑，一条近乎完美的宽约6-9公里的太阳反射光带便会沿着卫星轨道出现在水面上。
Because the ocean is never perfectly smooth or calm, however, the Sun’s reflection gets blurred. Incoming sunlight is scattered in all directions by waves. The Sun’s perfect reflection gets spread out across wider strip of the ocean, which looks washed-out compared to adjacent ocean areas.
因为海洋永远不可能是风平浪静的，所以太阳的反射光会变得模糊。入射的太阳光被波浪分散到各个方向。本应完美的太阳反射光在海面上蔓延成宽广的带状区域，比起邻近海域看起来像是褪色了一样。
Why is oil visible in sunglint?
Oil smoothes the surface of the water, dampening small waves and ripples. This smoothing changes the way the ocean reflects sunlight; in a sense, it makes the water a better mirror.
为什么可以在日光返辉中看到油污？
油污使得水面变的平滑，抑制了细浪和涟漪。这种平滑改变了海面反射日光的方式；在某种意义上说，它让水面更接近于一面镜子。
Rough water blurs the Sun’s reflection by reflecting and scattering light in many directions (left). Oil smoothes the water surface, making it a better mirror: more sunlight is reflected back to the observer (the satellite) at the same angle as the incoming sunlight (right). If the oil is located near where the Sun’s reflection would appear in the image, the mirror-like reflection makes the oil-covered water look brighter than clean water. (NASA image by Robert Simmon.)
粗糙的水面通过对光线进行反射和多角度的散射使得太阳的反射光变得模糊（左图）。油污使水面变得平滑，让它更接近于一面镜子：更多的入射日光被反射回处于同一角度的观测器（卫星）。如果油污位于靠近图像中会发生日光反射的区域，镜面反射会使得覆盖油污的水面比干净水面更为明亮。（NASA，制图：罗伯特·西蒙）
If the oil is located very close to the spot where the Sun’s reflection would appear, it usually looks brighter than nearby clean water in the MODIS images we routinely publish. However, if the oil is within the sunglint area but farther away from the precise spot where the Sun’s reflection would be, the oil-covered areas may look darker than the surrounding clearer water. Very thick oil may be visible outside of the sunglint region.
在我们定期发布的MODIS图像中，如果油污非常靠近会出现日光反射的地方，它总是比周围的干净水域要明亮。然而，如果油污虽处于日光返辉区，但是远离日光反射的确切位置，那么覆盖油污的水面会比周围清澈的水面更加暗淡。非常厚的油污即使是在日光返辉区之外也能被观测到。
How do you know what is oil and what isn’t?
Leaked, manmade oil is not the only thing that can cause variations in the brightness of the Sun’s reflection off the ocean. When a leak is known to have occurred and has been observed through other means, it is easier to conclude that variations in brightness within the sunglint region are oil, especially in the open ocean.
你们是怎么分辩油污的呢？
泄漏的人造石油并不是唯一可以导致海面的日光反射发生亮度变化的事物。当已经确定、并且通过其他手段观测到有泄漏发生之后，就很容易断定在日光返辉区发生亮度变化的是油污，尤其是在公海。
Coastal environments are especially challenging because sediment, river runoff full of organic matter, and complex currents, can also change the reflection in the sunglint area. In these situations, you have to be more cautious about concluding a feature is manmade oil.
海岸环境是特别具有挑战性的，因为泥沙、充满有机物的河川径流以及复杂的水流，都可以改变日光返辉区内的反射。在这种情况下，你必须更加谨慎地来判断某些特征是否是人造石油的。
Muddy water, naturally occurring plant oils and organic debris, and complex current patterns make it difficult to identify oil slicks in photo-like images. Some of the bright streaks in this July 9 image are oil, but others may not be. (NASA image courtesy MODIS Rapid Response Team.)
泥浆水、天然植物油脂和有机废料，以及复杂的水流图案使得难以在照片级图像中辨认浮油。在这张7月9日的图像中，某些明亮的条纹是油污，但有些则不是。（NASA，MODIS快速反应小组供图.）
Although MODIS satellite images cover the entire Gulf of Mexico every day, they have their limitations in observing surface oil slicks, which is why scientists and disaster responders are using a combination of photo-like satellite images, radar images, aerial photos, and observations from boats and the shore to document the size and spread of the Gulf of Mexico oil leak.
尽管每天的MODIS卫星图像覆盖整个墨西哥湾，它们也有观测水面浮油的局限性，这就是为什么科学家和灾害响应人员们使用照片级卫星图像、雷达图像、航空照片以及从海上和岸上观测相结合的方式来归档墨西哥湾石油泄漏的大小和扩散情况。
译注1：中分辨率成像光谱仪
译注2：美国航太总署
