The first detailed maps of global forest change

Posted by Matt Hansen and Peter Potapov, University of Maryland; Rebecca Moore and Matt Hancher, Google

Most people are familiar with exploring images of the Earth’s surface in Google Maps and Earth, but of course there’s more to satellite data than just pretty pictures. By applying algorithms to time-series data it is possible to quantify global land dynamics, such as forest extent and change. Mapping global forests over time not only enables many science applications, such as climate change and biodiversity modeling efforts, but also informs policy initiatives by providing objective data on forests that are ready for use by governments, civil society and private industry in improving forest management.

In a collaboration led by researchers at the University of Maryland, we built a new map product that quantifies global forest extent and change from 2000 to 2012. This product is the first of its kind, a global 30 meter resolution thematic map of the Earth’s land surface that offers a consistent characterization of forest change at a resolution that is high enough to be locally relevant as well. It captures myriad forest dynamics, including fires, tornadoes, disease and logging.

Global 30 meter resolution thematic maps of the Earth’s land surface: Landsat composite reference image (2000), summary map of forest loss, extent and gain (2000-2012), individual maps of forest extent, gain, loss, and loss color-coded by year. Click to enlarge

The satellite data came from the Enhanced Thematic Mapper Plus (ETM+) sensor onboard the NASA/USGS Landsat 7 satellite. The expertise of NASA and USGS, from satellite design to operations to data management and delivery, is critical to any earth system study using Landsat data. For this analysis, we processed over 650,000 ETM+ images in order to characterize global forest change.

Key to the study’s success was the collaboration between remote sensing scientists at the University of Maryland, who developed and tested models for processing and characterizing the Landsat data, and computer scientists at Google, who oversaw the implementation of the final models using Google’s Earth Engine computation platform. Google Earth Engine is a massively parallel technology for high-performance processing of geospatial data, and houses a copy of the entire Landsat image catalog. For this study, a total of 20 terapixels of Landsat data were processed using one million CPU-core hours on 10,000 computers in parallel, in order to characterize year 2000 percent tree cover and subsequent tree cover loss and gain through 2012. What would have taken a single computer 15 years to perform was completed in a matter of days using Google Earth Engine computing.

Global forest loss totaled 2.3 million square kilometers and gain 0.8 million square kilometers from 2000 to 2012. Among the many results is the finding that tropical forest loss is increasing with an average of 2,101 additional square kilometers of forest loss per year over the study period. Despite the reduction in Brazilian deforestation over the study period, increasing rates of forest loss in countries such as Indonesia, Malaysia, Tanzania, Angola, Peru and Paraguay resulted in a statistically significant trend in increasing tropical forest loss. The maps and statistics from this study fill an information void for many parts of the world. The results can be used as an initial reference for countries lacking such information, as a spur to capacity building in such countries, and as a basis of comparison in evolving national forest monitoring methods. Additionally, we hope it will enable further science investigations ranging from the evaluation of the integrity of protected areas to the economic drivers of deforestation to carbon cycle modeling.

The Chaco woodlands of Bolivia, Paraguay and Argentina are under intensive pressure from agroindustrial development. Paraguay’s Chaco woodlands within the western half of the country are experiencing rapid deforestation in the development of cattle ranches. The result is the highest rate of deforestation in the world. Click to enlarge

Global map of forest change: http://earthenginepartners.appspot.com/science-2013-global-forest

If you are curious to learn more, tune in next Monday, November 18 to a live-streamed, online presentation and demonstration by Matt Hansen and colleagues from UMD, Google, USGS, NASA and the Moore Foundation:

Live-stream Presentation: Mapping Global Forest Change

Live online presentation and demonstration, followed by Q&A

Monday, November 18, 2013 at 1pm EST, 10am PST

Link to live-streamed event: http://goo.gl/JbWWTk

Please submit questions here: http://goo.gl/rhxK5X

For further results and details of this study, see High-Resolution Global Maps of 21st-Century Forest Cover Change in the November 15th issue of the journal Science.

Building A Visual Planetary Time Machine

Posted by Randy Sargent, Google/Carnegie Mellon University; Matt Hancher and Eric Nguyen, Google; and Illah Nourbakhsh, Carnegie Mellon University

When a societal or scientific issue is highly contested, visual evidence can cut to the core of the debate in a way that words alone cannot — communicating complicated ideas that can be understood by experts and non-experts alike. After all, it took the invention of the optical telescope to overturn the idea that the heavens revolved around the earth.

Last month, Google announced a zoomable and explorable time-lapse view of our planet. This time-lapse Earth enables you explore the last 29 years of our planet’s history — from the global scale to the local scale, all across the planet. We hope this new visual dataset will ground debates, encourage discovery, and shift perspectives about some of today’s pressing global issues.

This project is a collaboration between Google’s Earth Engine team, Carnegie Mellon University’s CREATE Lab, and TIME Magazine — using nearly a petabyte of historical record from USGS’s and NASA’s Landsat satellites. And in this post, we’d like to give a little insight into the process required to build this time-lapse view of our planet.

Previews of the phenomena visible in these time-lapses.

First we'll describe Google’s Earth Engine system for deriving the time-series imagery. Second, we'll tell you more about CMU’s open-source “Time Machine” software for creating and streaming large, explorable time-series imagery.

Annual Composites: Distilling a Massive Dataset

Google Earth Engine brings together the world's scientific satellite imagery — over a petabyte of multispectral imagery recording over 40 years of history — and makes it available online with tools that scientists, independent researchers, and nations can use to mine this massive warehouse of data to detect changes, map trends and quantify differences on the Earth's surface using Google’s computational infrastructure. Today, the platform is used to monitor the Amazon and estimate forest carbon in Tanzania, among hundreds of other partners developing new uses for the technology.

Using Earth Engine, we first built annual global mosaics at a resolution of 30 meters per pixel for each year from 1984 through 2012. We started with a total of 2,068,467 scenes from the Landsat 4, 5, and 7 satellites, comprising 909 terabytes of data. The Earth’s atmosphere is a constantly-shifting sea of clouds, so in order to assemble a seamless cloud-free view of each year we analyzed all the images available at each location and used a simple cloud model to separate out the clouds from the ground. To help correct for atmospheric and seasonal effects, we used an additional 20TB of data from the MODIS MCD43A4 product to build a cloud-free low-resolution model of the Earth over time. We combined all this to produce a statistical estimate of the color of each pixel for every year for which data was available. Producing the final 29 global mosaics took a bit less than a day and consumed approximately 260,000 core-hours of CPU.

Some areas of the planet are almost perpetually cloudy, obscuring satellite views. In addition, before the more capable Landsat 7 began operating in 1999, coverage in some areas of the world was sparse, particularly in Asia, for various operational and technological reasons. We wrestled with how best to visualize areas with missing or cloud-obscured images from each year. In the end, after much experimentation, we chose to simply interpolate between valid image years. Other techniques, such as greying out invalid data, created distractingly large artifacts, visually drowning out the valid information. However, the downside with the approach we have taken is that it can be difficult to tell which data is original and which is interpolated. We are exploring the possibility of including a view that allows drilling down into the non-interpolated, original mosaics.

"Time Machine": An HTML5 Time-Series Exploration Tool

Once we had produced the final global images, we adapted the Carnegie Mellon CREATE Lab’s open-source “Time Machine” software, which enables authoring, streaming, and exploring very-high-resolution videos. Time Machine videos take advantage of the power of HTML5 and modern web browsers: they are streamed as multiresolution, overlapping video tiles and displayed in a web page by manipulating the HTML5