利用卫星图像计算储油罐的占用率
Calculating Oil Storage Tank Occupancy with Help of Satellite Imagery

原始链接: https://medium.com/planet-stories/a-beginners-guide-to-calculating-oil-storage-tank-occupancy-with-help-of-satellite-imagery-e8f387200178

TankerTrackers.com 通过油轮追踪、政府统计数据、EIA预测和卫星图像,绘制出一幅全面的“石油画像”,从而深入了解往往不透明的全球石油市场。其关键在于分析石油库存变化,利用Planet公司每日更新的卫星数据,对报告的产量和出口数据进行视觉验证,尤其针对那些石油活动缺乏透明度的国家。 这一过程包括利用谷歌地球建立参考点来测量油罐直径。油罐高度则通过石油公司的公开信息或图像分析确定,即通过侧面照片测量尺寸。油罐的储油量是通过分析阴影来估算的:油罐北侧的阴影指示油罐的总高度,而油罐内部的阴影则显示浮顶的深度(以及油罐的满油程度)。通过比较一段时间内的卫星图像,TankerTrackers.com 能够识别出库存波动,并将此数据与油轮运输情况交叉比对,从而判断石油是否正在被炼制或转移,最终更深入地了解全球石油趋势。

Hacker News上的一篇讨论围绕着利用卫星图像计算石油储罐占用率的文章展开。 一位评论员对人们使用电子表格进行图像测量表示惊讶,这解释了为什么一些人认为AI是一种潜在的更好(尽管有缺陷)的替代方案。其他人证实这项技术已经存在多年,一些人甚至将其应用于谷物仓储量的估算。 人们对这项技术的实际应用和盈利能力提出了疑问,提到了Orbital Insights的挣扎和Ursa Space Systems持续的服务。讨论还涉及浮顶罐的机械原理、其密封机制和消防系统。最后,简要地提到了冷战时期分析卫星图像上的板条箱以确定其内容物的“板条箱学家”。
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原文

At TankerTrackers.com, our mission statement is to present a bird’s eye view of the physical oil market with help of tanker-tracking, storage changes and official government statistics. We affectionately call it our “oil painting”. We gather a lot of data and analyze many events that will help professional and amateur traders on understanding the latest shift and trends in oil. We present four categories of data that appeal to our audience; those being oil tanker traffic, government statistics, EIA oil inventory forecasts and lastly, a visual confirmation of storage changes with the help of fresh satellite imagery. We chose Planet because of their global network of small satellites that provide access to daily updates in many locations of interest.

So, how and why does one put such technology to use? Well, let’s first cover the “why”. The global oil market is not entirely transparent. Many of the oil producing nations don’t like to voice their production, storage and export figures as it might put them in a bad spot at a negotiating table in for example Vienna, the HQ of OPEC (Organization of Petroleum Exporting Countries). If we can conclude with help of satellite imagery that a storage buildup has not occurred during a time when the country announced it would lower exports while maintaining production, then we will cross-check it with our tanker-tracking data and figure out whether the oil has gone into refining (into gasoline, for example) or if it was transferred by pipeline to a neighboring country’s storage/refinery.

As to “how” we use this technology, the answer is hidden in the shadows, quite literally.

Reference point: Diameter
First thing we need are reference points. The easiest to acquire is the diameter of the tank. You can use Google Earth’s ruler for that. Just drag and drop the line from one end of the tank’s rooftop to the other. Keep the line as straight as possible. In this example, we see 82 meters on most of the tanks we tested in the selected tank farm.

Reference point: Height

The second reference point is a bit trickier, but oh-so-necessary, and that is to find out the height of the storage tank. It is not obvious at first glance, but you have options; one of them even includes Googling the storage tank owner’s website, such as an oil company, refinery, storage facility, etc. Many post such information as it is part of their public marketing. However, if you are unable to find that information, then you can always try either contacting them or look for further clues. We never call around. We just Google or figure it out ourselves. Oh look, a photo of a storage tank in Ningbo, China is available on Google Earth! It actually shows the storage tank from its side. Lovely!

If we paste that image into a spreadsheet and crop it, we’ll get the width and height dimensions figured out. Make sure to not include the rear rim of the tank when cropping it. Just use the front. In our example, the width comes out as 2.57”, while height is 0.79”. We then crunch the numbers as shown below.

Psst! The alternative to this method is to actually hold up a ruler on your screen while no one is looking and just measure it quickly that way.

Next up, we’re calculating occupancy! By the time we’re done with this, you’ll quickly be able to approximate (with rough accuracy) how many barrels there are in each storage tank. To do so, we will need to rely on shadows. Below are some examples of what to look for. The shadow on the north side of the tank is a reference point for the total height of the tank whereas the shadow within the tank clues you in on the depth of the floating rooftop. What’s a floating rooftop, you wonder? In order for crude oil storage tanks to avoid a buildup of explosive gases, the rooftop rests on the oil directly. When oil enters the tank, the rooftop rises. When oil leaves the tank, the rooftop lowers. The more shadow you see within the tank, the less oil it contains.

Now that you got the gist of it, let’s have a look at a couple of images of Ningbo taken recently by Planet. One was taken on August 19th, 2017 and the other was taken exactly a month later. If you slide the center line to the left and right, you will spot the differences. Although not as clear as in the other images, we have a rough idea of the storage change over the past month between these three 837K barrel tanks.

Images ©2017 Planet Labs, Inc. cc-by-sa 4.0

If you look carefully, you will see that there has actually been NO CHANGE in the amount of barrels between these three storage tanks because the September image shows two half-full tanks along with an empty one, whereas August shows two empty tanks and a full one.

And that’s how it’s done.
TankerTrackers.com

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