Tag Archives: remote sensing

Satellite Image Time Lapse of Artisanal Mining in Peru

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My last post was about gold and mercury prices, and how we might measure their relationship. We would expect a relationship between prices of these metals because mercury is used in artisanal and small scale gold mining (ASGM). We may or may not see a signal in mercury prices related to ASGM, but we most definitely see the effects of ASGM on the landscape on a massive scale. Using the Landsat Annual Timelapse tool in Google Earth Engine, I created this animation showing the explosive growth of ASGM and associated deforestation near Huaypetue in the Madre de Dios region of Peru. Click on the image below to view the animation.

asgm landsat anim

You can see that beginning in the late 1990s, large areas around rivers turn from green (rain forest), to brown (cleared areas for mining). The trend seems to accelerate in the last 10-15 years. You can explore the region as it appears today in Google Maps:

And because it’s fun to play with Google maps, here is a striking oblique image of the region.

Zooming in a bit closer, seen from a plane flown by the Carnegie Airborne Observatory, the impacts of mining come into even sharper view:

The scenes on the ground look every bit as desolate as you would expect from the satellite and airborne imagery:

Embed from Getty Images

Embed from Getty Images Embed from Getty Images

If you are looking for more information on artisanal mining in Madre de Dios, this article in Nature is a good place to start. The Guardian has also been covering this region. This piece focuses on mercury use in mining and its toxic impacts.

A Bird’s Eye View of DC’s Solar Energy Potential

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A few years ago I had an idea for a smartphone app for homeowners considering installing rooftop solar panels. The homeowner would climb on top of the house and place the smartphone the roof. The app would use the phone’s gyroscope and compass to calculate the orientation of the roof’s plane in space, much like a geologist uses a Brunton compass to measure strike and dip of rock strata. Knowing the orientation and location of the roof, the app could make an estimate of solar insolation and help the homeowner work out the economics of the decision.

If this is such a good idea, why am I telling you all about it? Because I fear that it will soon be obsolete, and high resolution remote sensing data will be used to investigate initial feasibility of rooftop solar.

That is exactly what a website called Mapdwell Solar System is doing, at least in Washington DC. This company uses LiDAR to produce a very high resolution digital elevation model of the urban landscape. They use an algorithm to find all the rooftops, and for each one square meter area, they calculate the solar potential. The LiDAR data is so detailed that they can calculate the slope and orientation of roofs, as well as shading that occurs from buildings and trees. These one square meter pixels (color coded so that bright yellow equals higher solar potential) are overlaid on a satellite image of the city. Here’s what it looks like:

dc solar

The white circles are existing solar rooftop units.  To illustrate how this works, I decided to use Mapdwell to figure out what EPA could do with rooftop solar. I zoomed in and selected the headquarters complex (WJC Building and EPA East and West) in Federal Triangle. Here’s what it looks like:

epa solar

The yellow areas are where Mapdwell recommends putting solar photovoltaic panels. Bright yellow,  the optimal solar locations, are concentrated on the south facing parts of the roof. The most interesting part is the report generated that estimates cost of the system, federal tax credits, power output, payback time, and more. Here’s a summary from the EPA example:

mapdwell info

You can see that the system would cost about $10 million, but federal tax credits would reduce that by about $3 million. (Can federal buildings claim this tax credit?). It would have a capacity of 2.4 MW, and generate revenue from solar renewable energy certificates (SRECs) as well as offset electricity purchases from the grid. And the payback time would be 7 years with an internal rate of return of about 14%. That sounds like a good investment. It would also offset enough greenhouse gas emissions to be equivalent to planting 12,000 trees.

This is a very powerful tool. Unfortunately it’s only available in Washington, DC, and Cambridge and Wellfleet, MA, but hopefully your neighborhood will be covered before too long.