Posts Tagged ‘remote sensing’

Need access to thousands of historical aerials and topographic maps at your fingertips? Try

April 30, 2018 2 comments

Imagine having instant access to thousands upon thousands of historic aerial photographs and topographic maps to be able to examine change over time.  Thanks to a resource called Historic Aerials, you do have this wealth of information at your fingertips.  These aerials and maps, which go back 50, 60, and even 70 years or more, can be used for research, for instruction, for planning, and for other purposes.  Being in the field of geography and GIS education, I can think of many disciplines in which this can be used — urban and rural geography most certainly, but also biology, environmental science, city planning, history, agriculture, and also in GIS courses.  These resources foster spatial thinking about changes in time and space, from natural causes, such as volcanic eruptions or changes in river meanders, or from human causes, such as urbanization or the construction of reservoirs.  And given the connection that often exists between human and natural changes, sometimes these causes are intertwined–the construction of jetties along barrier islands often influences the naturally occurring longshore sediment transport and the migration of the islands themselves, as can be seen by comparing the historic to modern aerials of Ocean City, Maryland, for example.

The interface for the Historic Aerials is intuitive and provides tools that allow the user to compare USGS topographic maps of various years as well as the aerials themselves.  In the example below, I compare a 1958 with a 2009 aerial of a section of Grand Junction Colorado, before and after Interstate 70 and some surrounding housing was constructed.  You can also use the spotlight tool to “see back in time” for wherever you pan your cursor, and you can turn on the streets to see where  streets would one day be constructed on top of historical imagery.

The site comes from the Nationwide Environmental Title Research group, which has spent over 20 years collecting the worlds largest database of historical aerial images and topographical maps of the USA.  Their sources include USGS and USDA imagery, several private collections, and they are continually acquiring more. All the imagery they collect is orthorectified to provide the data in a searchable and precise geo-locatable format.  A print or digital image (for GIS users, GeoTIFF will be especially useful, delivered in lat-long coordinates, but JPG and PNG are also offered) of any of the maps or aerials is available.  In addition, a subscription service allows anyone to access the site with the following advantages: Full screen viewer, no advertising, PDF builder, quick JPEG downloads, and multiple user accounts.   I had a pleasant chat with the good people behind the site and found that their prices are quite reasonable.  Their FAQ, forum, and tutorials make it clear that they are committed to user success with these resources, and there are human beings behind this site to help as well.

Quite frankly, during my years working at the USGS, I always dreamed that my agency would create something like this.  Kudos to the HistoricAerials staff for making this a reality!


The interface for is quite intuitive and allows for fascinating investigations back in time for lands across the USA. 


Planet’s Imagery Now Viewable by the Public

January 29, 2018 2 comments

Back in 2014, we wrote about inexpensive and the miniaturization of remote sensing, as exemplified in Planet Labs then-new small satellites.  A year later, we wrote about the company’s (now called “Planet”) Open Region initiative with the United Nation to share imagery under a Creative Commons license.  As described in this National Geographic post, Planet has now created a web mapping tool that allows users to examine two million images, updated monthly.  The tool, called Planet Explorer Beta, contains images dating back to 2016, at anywhere from 3 to 40 meters.  My favorite feature so far on the Explorer Beta is the ability to drag-and-drop two images to create a swipe map, to compare changes over time for any given area.  If you create an account and log in, you can explore daily, rather than just monthly, imagery.  Whether logged in or not, the tool is an excellent and amazing resource for teaching and research.  It could also serve as a great way to introduce students and faculty to imagery and encourage them to go further and deeper with remote sensing.

As most of the readers of this blog are work in the field of GIS, they will want to know how to use this imagery in a GIS.  The viewer described above is just that–a viewer.  You can only view the images online.  To actually access the data for use in your GIS or remote sensing work, begin with Planet’s Documentation.  As Planet is a professional satellite image company, it comes as no surprise that users have a multitude of options from which to choose–bands, date and time, cloud cover, sun elevation and azimuth, rectification, data format, and much more.  The imagery is available via a Planet Explorer interface and a Data API, which requires installing a Python client.


Comparing imagery from two time periods in Colorado, USA, using Planet’s Planet Explorer Beta.

Accessing Landsat 8 Data through DevelopmentSeed’s Libra Portal

May 21, 2017 1 comment

Libra is a very useful browser for open Landsat 8 satellite imagery. You can use it to browse, filter, sort, and download imagery for the entire planet.  Libra was developed by DevelopmentSeed, an engineering team solving complex problems with open software and open data, and AstroDigital, a company focused on providing imagery analyzed in real time and streamed to applications via their API.

Libra’s map interface is one of the most straightforward and useful that I’ve ever seen for imagery as evidenced in the screenshot below.  On the interface, each circle on the map represents the number of available images at that location. Filters at the top of the map can be used to select a date range, cloud cover percentage, and sun azimuth angle. Bundled downloads are available within one week of the image being taken. Individual bands are available for all 2015 scenes.

Once your download is complete, the site organizers recommend Landsat-util for processing the raw image and getting it ready for publication and analysis.  Search results are powered by Landsat 8 Metadata API and images from USGS Earth Explorer. Downloads are provided via Google Earth Engine and Amazon Web Services.

More information and the official announcement about this resource can be found here.   Give it a try and let us know what you think.

Interface for the Libra Development Seed Landsat Site.

Interface for the Libra Development Seed Landsat Site.

New LandViewer Tool for Quickly Finding and Analyzing Satellite Imagery

May 7, 2017 2 comments

The LandViewer tool and data portal quickly and painlessly allows you to browse and access satellite imagery for the planet.  The tool, developed by the Earth Observing System Inc.’s Max Polyakov, currently features Landsat 8 and Sentinel 2 imagery with more image sets soon to arrive.  Landsat 8 carries two instruments: The Operational Land Imager (OLI) sensor includes refined heritage bands, along with three new bands: a deep blue band for coastal/aerosol studies, a shortwave infrared band for cirrus detection, and a Quality Assessment band. The Thermal Infrared Sensor (TIRS) provides two thermal bands. Sentinel 2 is an Earth observation mission developed by the ESA as part of the Copernicus Programme to perform terrestrial observations in support of services such as forest monitoring, land cover changes detection, and natural disaster management.

Using the LandViewer tool, you can quickly zoom on an interactive web map to your area of interest.  You can filter on geography and time, including cloudiness, sun angle, and other parameters. At the time of this writing, 18 filters such as Atmospheric Removal, Panchromatic, NDVI, Thermal Infrared, False Color, and more, are available so that you can obtain the band combinations most suitable to your analysis in the areas of agriculture, geology, or other applications. A very helpful image interpretation screen is available to help you choose the combination that are best for your analysis goals.  You can do some contrast stretching in the web tool itself.  Then after signing in to the site, you can download the images in GeoTIF for further analysis using your favorite GIS tools.

The tool was also reviewed on the Geoawesomeness web site, and I wholeheartedly agree with their sentiments expressed–this is one of the most useful and fastest satellite image portals I have used. It is useful for research but also, given its ease of use, can even be used effectively to teach concepts of remote sensing.  Give it a try and let us know in the comments section what you think.


Landsat scenes with band combinations possible for an area on the southwest side of Costa Rica.


Enhancements to Landsat Thematic Bands Web Mapping Application

November 6, 2016 Leave a comment

Last year, we wrote about the Landsat Thematic Bands Web Mapping Application, an easy-to-use but powerful teaching and research tool and data set. It is a web mapping application with global coverage, with mapping services updated daily with new Landsat 8 scenes and access to selected bands that allows the user to visualize agriculture, rock formations, vegetation health, and more.  The Time tool allows for the examination of changes over years, over seasons, or before and after an event.  The identify tool gives a spectral profile about each scene.  I have used this application dozens of times over the past year in remote sensing, geography, GIS, and other courses and workshops, and judging from the thousands of views that this blog has seen, many others have done the same thing.

If that weren’t all, the development team at Esri has recently made the tool even better–one can now save a time sequence or a band combination as a permanent URL that can be shared with others.  The flooding of 20 districts in August and September 2016 in Uttar Pradesh, India, for example, can be easily seen on this link that uses the application, with screenshots below.

Another example is the Fort McMurray summer 2016 wildfire in Alberta, Canada  – the user can change the time to see the region’s vegetation cover before and after fire, and the extent of the smoke during the fire.  Or, you can analyze a different band combination, as is seen here.

To do this, open the application.  Note that the application URL has been updated from the one we wrote about last year.  Move to an area of interest.  Select any one of the available thematic band renderers (such as agriculture, natural color, color infrared, and others available), or create your own band combination using build.  Then, turn on “time” to see your area of interest at different periods using your band combination.  Next, share this image with other people.   Simply click on any one of the social platforms (Facebook or Twitter) in the upper right, which will create a short link that can be shared.  When the person you send this link to opens it, the Landsat app will open in exactly the same state it was in before social platform tool was clicked.  Give it a try!


Landsat 8 Image for Allahabad India on 31 May 2016.


Harmonising UAS Regulations and Standards: Article Review

October 23, 2016 Leave a comment

A recent article in GIM International about harmonising UAS (Unmanned Aerial Systems, or UAVs (Unmanned Aerial Vehicles), or “Drone” technologies) regulations and standards is definitely worth reading, providing an excellent summary of this rapidly evolving sector of the geospatial industry.  The article, beginning on page 6, is in a special issue of GIM International dedicated exclusively to UAS, available here.  Peter van Blyenburgh summarizes developments in regulations and standardization in Europe, the USA, Japan, and China, and then provides some down-to-earth advice for companies who are seeing the potential for profits only but may not see the bigger picture about liability, regulations, and safety.  The GIM issue also includes articles about integrating UAS and multibeam echosounder data, multispectral and thermal sensors on UAVs, UAS applications in agriculture, and the article “Airborne laser scanning” provides an excellent introduction to the two main platforms:  fixed-wing and rotorcraft.

If I am reading the “tea leaves” correctly, in the world of education, just about every GIS program offered at a technical college and university will include at least one course in UAS technology and data by this time next year.  And I would expect that a whole host of online MOOCs and other courses will appear from universities, companies, and GIS organizations to help people effectively use these new tools and technologies.  I attended, for example, a multi-hour course at the recent Geo’Ed community college GIS conference on this topic.  This reinforced my opinion that while online courses and programs will be helpful, the face-to-face component, actually working with the software and hardware, is particularly useful when working with UAS:  There is no perfect substitute for rolling up one’s sleeves and working with these devices.

As publishing director Durk Haarsma states in his editorial for this special issue, UASs are disruptive technologies, because they are influencing so many geospatial fields and subfields, such as cadastral surveying, cultural heritage, and precision agriculture, just to name a few.  Because UAS influence how people in an increasing number of professions map and model the world, interpreting the data from those UAS is central to our book and this blog–understanding your data, and how they are obtained, is more critical than ever.


Launching a fixed wing UAV at the Geo’Ed conference, Louisville Technical College, Kentucky. Photograph by Joseph Kerski.  Video here and analyzing thermal imagery here.

Landsat Thematic Bands Web Mapping Application in ArcGIS Online

December 20, 2015 2 comments

Teaching remote sensing?  Or just want to understand remotely sensed imagery better?  The Landsat Thematic Bands web mapping application can serve as a very useful teaching, learning, and research tool.  It covers the entire planet and the map is updated daily with new Landsat 8 scenes.

You can access many band combinations and indices by hovering over the tools to the left of the map image and selecting among the following:

  • Agriculture: Highlights agriculture in bright green. Bands 6,5,2
  • Natural Color: Sharpened with 25m panchromatic band. Bands 4,3,2+8
  • Color Infrared: Healthy vegetation is bright red. Bands 5,4,3
  • SWIR (Short Wave Infrared): Highlights rock formations. Bands 7,6,4
  • Geology: Highlights geologic features. Bands 7,4,2
  • Bathymetric: Highlights underwater features. Bands 4,3,1
  • Panchromatic: Panchromatic image at 15m. Band 8
  • Vegetation Index: Normalized Difference Vegetation Index (NDVI). (Band5-Band4)/(Band5+Band4)
  • Moisture Index: Normalized Difference Moisture Index (NDMI). (Band5-Band6)/(Band5+Band6)

The Time tool for different indices at larger scales based on a user-selected location enables examination of changes over years or over seasons.  It also provides temporal profiles for NDVI (Normalized Difference Vegetation Index), NDMI (Normalized Difference Moisture Index) and an Urban Index, dating back to 1973.  The Identify tool enables access to information on the date, cloud cover, and a spectral profile about each scene.  The Bookmark tool allows access to interesting locations such as the “Eye of the Sahara” in Mauritania.

The application is written using Web AppBuilder for ArcGIS accessing image services using the ArcGIS API for JavaScript, with access to the following Image Services:

  • Landsat Multispectral on AWS – 8-band multispectral 30m resolution image services and functions that provide different band combinations and indices.
  • Landsat Pan-sharpened on AWS – Panchromatic-sharpened imagery; 4-band (Red, Green, Blue and NIR); 30m resolution.
  • Landsat Panchromatic on AWS – Panchromatic imagery; 15m resolution.

These services can also be accessed through the public Landsat on AWS group on ArcGIS Online.  Because you can add these services as layers to your own maps or are adding to maps made by others, or if you are simply using the above web mapping application as a standalone map, you truly have “the world at your fingertips” with these maps and apps.  But there is a third option: Use the Unlock Earth’s Secrets page, also useful for instruction, with the above application embedded in it, but also with explanatory text and featured places around the planet as they have changed through time.

Think of the above as solid introductory segments to help your students, customers, or stakeholders see the value in remote sensing.  These maps and applications require very little geospatial technology skills to use, but allow you to focus on building remote sensing concepts and principles while exploring some truly engaging content and places.

To dig deeper, delve into the many powerful remote sensing functions available in ArcGIS Desktop.  One source for engaging, hands-on activities, is Kathryn Keranen and Bob Kolvoord’s book Making Spatial Decisions Using GIS and Remote Sensing:  A Workbook.

Give these resources a try!

Landsat web application

Landsat web application in ArcGIS Online.