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Sensors and Journalism: ProPublica, Satellites and The Shrinking Louisiana Coast

Two months before the programmers journalists at ProPublica would be ready to go live with an impressive news app illustrating the huge loss of land along the Louisiana coast line, the development team gathered in their conference room above the financial district in Manhattan.

This was partly a show-off session and partly a review. Journalist-developers Brian Jacobs and Al Shaw pulled a browser up onto the glossy 46-inch screen and loaded up their latest designs. At first it appears to be simple satellite photography, spanning about 20,000 square miles, but the elegance hides a complicated process to pull layers of meaning from many rich data sets.

At the heart of the story is the fact that the Louisiana coastline loses land at a rate equivalent to a football field each hour. That comes to 16 square miles per year. The land south of New Orleans has always been low-lying, but since the Army Corps of Engineers built levees along the Mississippi after the huge 1927 floods, the delta has been losing ground. Previously, the river carried sediment down and deposited it to gradually build up dry land throughout the delta. The same levees that protect upstream communities also block that sediment from reaching the upstream river and floating down to become Louisiana coastline. Environmental researchers say that the energy industry’s canal-dredging and well-drilling have accelerated natural erosion. Together, the constricted river and the oil extraction have exacerbated the effect of sea level rises from climate change.

The loss of ground endangers people: The dry land used to provide protection to New Orleans’ people and businesses, because when storms like Hurricane Katrina sweep in from the Gulf Coast, they lose power as they move from the water to land. It’s therefore crucial to have a wide buffer between the sea and the city. Now, with 2,000 fewer acres of protective land, the state will have to spend more money building tougher, higher walls, flood insurance will be more costly, infrastructure could break and the people inside those walls risk death and injury at much higher rates. If the land-loss isn’t slowed the costs will get higher.

Satellites Clearly Show The Story

For this story, Al Shaw’s goal was to illustrate the scale and severity of the problem. Print journalists have written extensively on the story. But the forty years worth of remote sensing data available from NASA’s Landsat satellites helped the ProPublica journalists to show the story with immediate power and clarity. They processed Landsat 8 sensing data themselves and drew on the US Geological Survey’s interpretations of data from earlier Landsat craft.

The project combines a high-level view with eight zoomed-in case studies. The scene of land, marsh and water known locally as the Texaco Canals forms one of the most dramatic examples. Starting with data collected from aerial photography in the 1950s and ending with 2012 satellite data, the layered maps show how the canals sliced up the marshlands and the relocated soil stopped sediments replenishing the land. The result is an area that starts mostly as land, and ends mostly as open water. Contemporary and archival photos complement the birds-eye view with a human level perspective.

This is Satellite Sensing’s Learning Curve

At this point, we need to reveal a conflict of interest. In February 2014 The Tow Center provided training to four journalists from ProPublica. Lela Prashad, a remote sensing specialist who has worked with NASA led a two day workshop covering the fundamental physics of satellite sensing, a briefing on the different satellite types and qualities, where to find satellite data and the basics of how to process it. ProPublica news apps director Scott Klein had been at a Tow Center journalistic sensing conference eight months earlier to see a presentation by Arlene Ducao and Ilias Koen on their satellite infra-red maps of Jakarta and saw that ProPublica’s innovative newsroom might be able to use remote sensing to cover some of their environmental stories in new ways.

The ProPublica journalists, to produce this work, learnt the physics and applications of remote sensing technology. The earth’s surface pushes energy out into the atmosphere and space – some is an immediate reflection of the sun’s rays, some is energy absorbed earlier. Human sources like city lights and industrial activity also produce emissions. Energy waves range from the high-frequency, short wavelength gamma-rays and x-rays, through ultra-violet then into the visible spectrum (what human eyes sense) and on towards the longer wavelengths of infra-red, microwave and radio.
Satellites flown by NASA (and increasing numbers of private companies) point cameras towards Earth taking pictures of the energy which passes through the atmosphere. Those are the ultraviolet, visible and infrared bands. (The various generations of satellites have had different capabilities. As they develop, they have recorded Earth with more detail and pass overhead more frequently.)
Those scenes, when processed, can reveal with great accuracy the materials that form Earth’s surface. The exact hue of each pixel represents the specific substance below. Geologists needing to identify types of rock take advantage of the fact that, for example, sandstone reflects a different combination of energy waves than granite. Food security analysts can assess the moisture, and therefore the health, of a country’s wheat crop – helping them predict shortages (and speculators predict pricing). ProPublica is showing the Louisiana coast-line change over time from dry land, to marsh, to open water.

The US Geological Survey (USGS) makes its data available through a series of free online catalogues. Registered users can nominate the area they are interested in, pick a series of dates and download image files which include all the available energy bands. Crucially, those image files include the Geographic Information Systems (GIS) meta-data that allow the journalists to precisely match the pixels in data files to known locations.


How The Developers Built it

Brian Jacobs learned how to to reproduce and combine the information in an accessible form for ProPublica’s online audience. The opening scene of the app has eight layers. The top one uses scanned copy of a 1922 survey map owned by the USGS and scanned by the Louisiana State University library. Jacobs pulled it into his mapping software to match the geographic features with GIS location data and used photoshop to prepare it for online display; cutting out the water and normalizing the color.

The bottom layer displays the 2014 coastline – stitched together from six Landsat 8 tiles, including many steps of processing. Jacobs picked out images from satellite passes when the skies were free from cloud cover. After pulling in the image tiles from the infrared and true-color bands and merging them together, Jacobs normalized the distortions and color differences so the separate images would mosaic consistently.
Working with the command-line tools, GDAL (a geospatial library) and ImageMagick (an image editing suite), he prepared them for online display. Pictures of the Earth’s curved surface need to be slightly warped to make sense on a flat images, the types of warps are called projections. The raw USGS images come in the space industry’s WGS84 projection standard, but the web mostly uses Mercator. (Here’s Wikipedia‘s explanation, and xkcd’s cartoon version.)

Researchers who work with remote sensing have a specific language and sets of practices for how they treat color in their visualizations. The ProPublica journalists adopted some of those practices, but also needed to produce their work for a lay audience. So, although the features on ProPublica’s maps are easily recognizable, they are not what’s known as ‘true color’. When viewers look closely at the bottom layer, it’s clear that these are not simply aerial photographs. In comparison to satellite photography displayed via Google maps, the ProPublica layer has a much sharper contrast between land and water. The green pixels showing land are vibrant, while the blue sections showing water are rich, deep blues.

The color palette is, in fact, a combination of two sets of satellite data: The water pixels are interpreted from Landsat’s infrared and green bands, while the land pixels come from Landsat ‘true color’ red, green and blue bands, with extra sharpening from the panchromatic band (panchromatic appears as shades of gray, but can be interpreted to color). At 30m/pixel, Landsat’s color bands are lower resolution than its 15m/pixel panchromatic band.

Step By Step Frames

This is a detail of a single tile, in a single band, but color-corrected.

A detail of a single tile in the true-color space, somewhat color-corrected.

At this point, the developers have stitched together multiple tiles of their area, and combined images from many wavelength bands, a process known as pansharpening.

At this point, the developers have stitched together multiple tiles of their area, and combined images from true-color and panchromatic bands, a process known as pansharpening.

The water mask

This is the mask that ProPublica produced from the near-infrared and green bands. It’s used to make a distinction between the areas of land and water.

Pansharpened, zoomed

This frame shows the final result of ProPublica’s satellite image processing. At this point the images have been pansharpened and the water layer has been included from the near IR and green band.

The final view that ProPublica showed their users.

This shows the underlay for ProPublica’s case studies. This land pixels combine true color bands and the high-resolution panchromatic band. The water pixels come from the infrared and green bands.

Google satellite view, zoomed

The same area, as shown in Google maps’ satellite view. Mostly, it uses true-color satellite imagery for land, and bathymetry data for water.

A detail of the USGS map. Each color represents a period of land loss. ProPublica extracted each period to separate layers in their interactive map.

A detail of a USGS map of the region. Each color represents a period of land loss. ProPublica extracted each the pixels of period to separate layers into an interactive map.

The other layers come from a range of sources. In the opening scene, viewers can bring up overlays of the human building associated with the oil and gas industry: including the wells and pipelines, the dredged canals and the levees that protect the homes and businesses around the coastline.

When users zoom in to one of ProPublica’s seven case studies, they can scrub through another 16 layers. Each one shows a slice of time when the coast line receded. A layer of olive green pixels indicates the remaining dry land. The data for these 16 layers came from researchers at the US Geological Survey (USGS) who had analyzed 37 years of satellite data combined with historical surveys and mid-century aerial photography. ProPublica’s worked with John Barras at the USGS, a specialist who could draw on years of his own work and decades of published studies. He handed over a large geo-referenced image file exported from the software suite ERDAS Imagine. Each period’s land loss was rendered in a separate color

The Amount of Time, Skill and Effort

Scott Klein described this project as one of ProPublica’s larger ones, but not abnormally so. His team of developer-journalists release around twelve projects of this size each year, as well as producing smaller pieces to accompany work by the rest of ProPublica’s newsroom.

For six months, the project was a major focus for Al Shaw and Brian Jacobs. Both Shaw and Jacobs are young, highly skilled and prized developer-journalists. Al Shaw has a BA, and is also highly active in the New York’s hacks/hackers community. Brian Jacobs is a Knight-Mozilla Fellow working at ProPublica, with a background that includes a year at MIT’s Senseable City Lab and four years as a UI designer at Azavea, a Philadelphia based geospatial software company. They worked on it close to full time, with oversight from their director Scott Klein. During the later stages, ProPublica’s design director David Sleight advised on the interaction design, hired a freelance illustrator and led user-testing. ProPublica partnered with The Lens, a non-profit public-interest newsroom based in New Orleans, whose environmental reporter Bob Marshall wrote the text. The Lens also sourced three freelance photo researchers and photographers for ProPublica.

ProPublica Have Shared Their Tools

To produce the work, ProPublica had to extend the ‘simple-tiles’ software library they use to publish maps – a process that soaked up months of developer time. They’ve now open-sourced that code – a move which can radically speed up the development process for other newsrooms who have skilled developers. In common with most news organizations, the interactive maps ProPublica has historically published have used vector graphics: which display as outlines of relatively simple geographic and city features like states, roads and building footprints. This project renders raster (aka bitmap) images, the kind of file used for complicated or very detailed visual information.

ProPublica’s explanation about their update to simple-tiles is available on their blog, and the code is available via github.

Their Launch

ProPublica put the app live on the 28th of August, exactly nine years after the Hurricane Katrina made New Orleans’ mayor order the city’s first ever mandatory evacuation.

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