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Posts Tagged ‘raster’

Daily Satellite Imagery for Planet Earth

December 1, 2014 1 comment

In this blog, we have written about the revolution occurring in the remote sensing world, centered on inexpensive and crowdsourced remote sensing. As described in this TED talk from Planet Labs’ Will Marshall, Planet Labs has launched small satellites of the dimensions 10 x 10 x 30 cm, weighing 4 kg, which can take images at 10 times higher resolution than conventional large satellites.  Early in 2014, the International Space Station launched 28 of these small satellites.  They plan to launch more than 100 that will image the Earth from a single orbital plane as the planet rotates beneath it.  Will refers to this system as a “line scanner for the planet.”

While our book and this blog discuss geotechnologies from a technical point of view, we also highlight the societal implications of these innovations.  Planet Labs’ work fits in well with these themes, because they are not only technically innovative, but their goal is to democratize remote sensing data.  They are asking:  “If you had access to imagery for the whole planet on a daily basis, what would you do with it?” Every point on the planet will be imaged every day with their platform.

And while the partnerships and avenues of dissemination data are still being worked out, this and similar efforts in the remote sensing world will surely impact data availability, crowdsourcing, copyright, privacy, decision-making, and other topics important to science, education, and society, in the months and years ahead.

 

Planet Labs:  Imagery and its democratization

Planet Labs: Imagery and its democratization.

 

 

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High-resolution SRTM elevation data to be released globally

October 12, 2014 1 comment
Comparing SRTM data resolutions

Comparing SRTM data spatial resolution:  90 meters on the left, 30 meters on the right.

High-resolution elevation data from the Shuttle Radar Topography Mission-Level 2 (SRTM-2), previously only available for the USA, will be made publicly available over the next 12 months, the White House announced recently at the United Nations Heads of State Climate Summit. The first elevation data set to be released will be over the African continent and is available on the United States Geological Survey’s Earth Explorer website, by choosing the “SRTM 1 Arc-Second Global” data set, with future regions to be released within the coming year.

“I look forward to the broader impact that the release will have on the global scientific and capacity building community,” said National Geospatial-Intelligence Agency (NGA) Director Letitia Long.  Until now, SRTM data was only publicly available at a lower 90-meter resolution (see above image). The newly-released global 30-meter SRTM-2 dataset will be used worldwide to improve environmental monitoring, climate change research including sea-level rise impact assessments, and local decision support, the White House said.

The SRTM mission began in 2000 as a venture between NASA and NGA that used a modified radar system on board the Space Shuttle Endeavour to acquire elevation data for over 80% of the Earth’s land mass. The Department of Defense and intelligence community continues to use this topographic data for multiple applications – from developing navigation tools and supporting military operations, to geological and environmental purposes.  In August 2014, Long authorized the removal of the Limited Distribution caveat from the SRTM-2 dataset, making it available to the public on a phased-release schedule. The 30-meter topographic dataset was then sent to USGS for public distribution.

When I heard Shuttle pilot Dom Gorie speak about his work with the SRTM at a GIS conference about 10 years ago, it was one of the most memorable keynote addresses I have ever heard.  I look forward to investigating this new data set and the delivery mechanism.  Keep an eye on this blog for further updates.

 

The National Atlas of the USA is Disappearing

July 6, 2014 2 comments

One of the most useful sites of the past 15 years for GIS users, in my judgment, has been the National Atlas of the United States.  It contains a “map maker” that allows you to create online maps of climate, ecoregions, population, crime, geology, and many other layers, and a “map layers” repository that houses all of the raster and vector data layers that are displayable in the map maker.  All of those hundreds of layers are downloadable in standard formats that are easy to use with GIS.

Sadly, the National Atlas is scheduled to disappear on 30 September 2014.  According to the transition FAQ, “the National Atlas and The National Map will transition into a combined single source for geospatial and cartographic information.  This transformation is projected to streamline access to maps, data and information from the USGS National Geospatial Program (NGP).  This action will prioritize our civilian mapping role and consolidate core investments while maintaining top-quality customer service.”  Thus, the National Map is scheduled to be the content delivery mechanism for the National Atlas content.

But, data users take note:  Not all of the National Atlas content is migrating to the National Map.  According to the FAQ’s question of “Will I still be able to find everything from the National Atlas on The National Map web site”, the answer is, “No. Most National Atlas products and services that were primarily intended for a broad public audience as well as thematic data contributions from outside the National Geospatial Program (NGP) will not be available from nationalmap.gov.”

I think this is most unfortunate news.  In my opinion, and that of many students and educators that I work with in courses and institutes, and the other data users I have worked with over the years, the National Map is almost as clunky and difficult to use as it was 10 years ago.  I use it frequently because it is still one of the richest sources of data, but it is by no means easy to obtain that data.  And equally importantly, it serves a different audience than the National Atlas does.   Yes, the National Atlas viewer is dated, but it requires little bandwidth, making it accessible to schools and other institutions contending with poor connectivity. How much effort is required just to leave national atlas alone and leave it online, with an understanding that it will not be updated?

In an era where more geospatial data are needed, not less, and improved geographic literacy is increasingly critical to education and society, the disappearance of the National Atlas seems like a giant step backward.

National Atlas website with Map Maker and just a few of the many data layers available.

National Atlas website with Map Maker and just a few of the many data layers available.

Spatial Analyst videos describe decision making with GIS

I have created a series of 22 new videos describe decision making with GIS, using public domain data.  The videos, which use the ArcGIS Spatial Analyst extension, are listed and accessible in this YouTube playlist.  Over 108 minutes of content is included, but in easy-to-understand short segments that are almost entirely comprised of demonstrations of the tools in real-world contexts.  They make use of public domain data such as land cover, hydrography, roads, and a Digital Elevation Model.

The videos include the topics listed below.  Videos 10 through 20 include a real-world scenario of selecting optimal sites for fire towers in the Loess Hills of eastern Nebraska, an exercise that Jill Clark and I included in the Esri Press book The GIS Guide to Public Domain Data and available online.

New Spatial Analyst videos explain how to make decisions with GIS.

New Spatial Analyst videos explain how to make decisions with GIS.

1)  Using the transparency and swipe tools with raster data.
2)  Comparing and using topographic maps and satellite and aerial imagery stored locally to the same type of data in the ArcGIS Online cloud.
3)  Analyzing land cover change with topographic maps and satellite imagery on your local computer and with ArcGIS Online.
4)  Creating a shaded relief map using hillshade from a Digital Elevation Model (DEM).
5)  Analyzing a Digital Elevation Model and a shaded relief map.

6)  Creating contour lines from elevation data.
7)  Creating a slope map from elevation data.
8)  Creating an aspect (direction of slope) map from elevation data.
9)  Creating symbolized contour lines using the Contour with Barriers tool.
10)  Decision making using GIS:  Introduction to the problem, and selecting hydrography features.

11) Decision making using GIS:  Buffering hydrography features.
12)  Decision making using GIS:   Selecting and buffering road features.
13)  Decision making using GIS:  Selecting suitable slopes and elevations.
14)  Decision making using GIS:  Comparing Boolean And, Or, and Xor Operations.
15)  Decision making using GIS:   Selecting suitable land use.

16)  Decision making using GIS:  Selecting suitable land use, slope, and elevation.
17)  Decision making using GIS:   Intersecting vector layers of areas near hydrography and near roads.
18)  Decision making using GIS:  Converting raster to vector data.
19)  Decision making using GIS:  Final determination of optimal sites.
20)  Creating layouts.

21)  Additional considerations and tools in creating layouts.
22)  Checking Extensions when using Spatial Analyst tools.

How might you be able to make use of these videos and the processes described in them in your instruction?

Historical and seasonal Landsat data: WELD Resource

The Web-enabled Landsat Data (WELD) project generates 30-meter composites of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) terrain corrected (Level 1T) mosaics at weekly, monthly, seasonal and annual periods for the conterminous United States (CONUS) and Alaska. These mosaics provide consistent data that can be used to derive land cover as well as geophysical and biophysical products for regional assessment of surface dynamics and to study Earth system functioning.

Landsat WELD resource

Landsat WELD resource

A collaboration between the United States Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center and academic partner South Dakota State University Geographic Information Science Center of Excellence, this is an excellent resource for all who seek to compare land use through time and through seasonal variation using Landsat data in the continental USA and in Alaska.  The WELD documentation site describes the WELD products on the site, known issues, and future plans.

WELD products are available as custom GeoTiff subsets via a new interactive web ordering system and as tiled HDF products via FTP.  I found the site fairly intuitive, simple, and straightforward to use.  Its products are directly importable into GIS software and hence it provides much more than visualizations, but rather, products useful to the GIS analyst.  The “good news, bad news” is that the GIS data user is confronted with an array of Landsat sites from which they may obtain data.  Each has its own interface and formats, but the situation is still far better than 10 years ago when nearly all of it was either for fee or difficult to obtain. Because it is not well linked to other sites, the WELD site is difficult to “stumble across” unless the data user is familiar with the acronym.  However, it is well worth a visit as it is one of the most intuitive and resource-rich.

Maps as representations of reality: The deciduous-coniferous tree “line”

November 5, 2012 3 comments

One of the themes running through our book The GIS Guide to Public Domain Data is that maps are representations of reality.  While almost everyone reading this statement is likely to agree with it, in the fast-paced world that GIS analysis and creating maps has become, it is easy to lose sight of this fact when staring at tables, maps, and imagery.  In a recent video, I discuss just one place where care needs to be made in making decisions based on spatial data.  In the video, observe my surroundings as I stand near the traditional “line” that divides the deciduous forest to the south from the coniferous forest to the north in North America. Is the “line” really a line at all, or is it better described as a gradual change from deciduous to coniferous as one travels north?  Is that vector line then better symbolized as a “zone”, or is vegetation better mapped as a raster data set, with each cell representing the percentage of deciduous and coniferous trees?

How many other data sets do we tend to see as having firm boundaries, when the boundaries are not really firm at all in reality?  How does that affect the decisions we make with them?  Even the boundary between wetlands and open water were originally interpreted based on land cover data or a satellite or aerial image.   As we state in the book, even contour lines were often interpreted originally from aerial stereo pairs.  And each data set was collected at a specific scale, with certain equipment and software, at a specific date, and within certain margins of error that the organization established.  Maps are representations of reality.  They are incredibly useful representations to be sure, but care needs to be taken when using this or any abstracted data.