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Posts Tagged ‘remote sensing’

Sensing air quality while photographing streets

October 15, 2018 1 comment

As described in an article in Business Wireair quality will be monitored on Google’s Street View vehicles starting with 50 cars in California.   Resulting from an agreement between Google and Aclima, carbon dioxide (CO2), carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2), ozone (O3), and particulate matter (PM2.5) will be sensed initially.  “This snapshot data will be aggregated and designated with a representativeness indicator and will be made available as a public dataset on Google BigQuery. The complete dataset will be available upon request to advance air quality science and research.”

Because Google Street View vehicles are already collecting in many countries (though not all, for quite a variety of reasons, as we mention in our book), monitoring air quality seems like an efficient partnership to gather this information.  Doing so by vehicle rather than via a standard fixed-position air quality monitoring station adds the benefit of monitoring in many areas, and over many time periods throughout the day in those areas.   One possible challenge in assessing the resulting data is that the points will be gathered in different places, with little repeated detection in the same place at the same time.  In a very real sense, the Google Street View vehicles become part of the Internet of Things.  I wonder if by having the air quality sensors on the vehicles whether Google will be sending the vehicles out more often than their standard street view updates require; i.e. whether the new goals will actually influence the schedule of the data gathering itself.   In a very real sense, if that happens, it is another example of the disruptive transformational nature of modern web GIS.

I suspect this is only the beginning.  Given increased demand for data at finer and finer scales, it only makes sense for government organizations, private companies, and nonprofit organizations to think about the existing platforms and mechanisms by which data is already collected, and broker relationships to attach their own data gathering to these existing platforms.  It is conceivable that the Street View vehicles could be outfitted with additional sensors, and, in a short time from now, the vehicles will be analogous to smartphones:  Because smartphones can do so much more than make calls and receive calls, calling has become only a minor part of their functionality.  Perhaps in only a year or two, people will have to be reminded that the Street View vehicles can actually take photographs of the neighborhoods they are passing through.

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Imaging Spectrometer data from NASA AVIRIS

June 11, 2018 1 comment

The NASA AVIRIS mission has generated imaging spectrometer data for many areas of the USA since the 1990s.  The AVIRIS download portal for data from 2006 onward is on a node at NASA, here.  The AVIRIS sensor collects data that can be used for characterization of the Earth’s surface and atmosphere from geometrically coherent spectroradiometric measurements. This data can be applied to studies in the fields of oceanography, environmental science, snow hydrology, geology, volcanology, soil and land management, atmospheric and aerosol studies, agriculture, and limnology.  Applications under development include the assessment and monitoring of environmental hazards such as toxic waste, oil spills, and land/air/water pollution. With proper calibration and correction for atmospheric effects, the measurements can be converted to ground reflectance data which can then be used for quantitative characterization of surface features. In short, AVIRIS can collect in over 200 bands and therefore it can help analysts work out details such as vegetation health, or even species type, from the data.

The AVIRIS portal, presented in a Google map with popups with download links, as well as the  metadata file (in plain text format, available here)  both look very dated.  But this is a case where we encourage the user to give it a try–the portal may not look modern, but the data behind the portal is incredibly useful.   One can toggle data layers in the right hand corner of map to show All AVIRIS data or the Attrib. Filtered data (data that meets the attribute criteria but ignores the spatial filter).  One can also bound a box on the map, which has long been a favorite feature of mine on data portals, using the red rectangle to activate.  To update the spatial filter, click the “Update Map” button below the map.   The files are not streamed, but must be downloaded; perhaps because of their large size (typically over 1 GB).  Again, think “old school” formats – zip files and TAR files, but again, the data are plentiful and useful.   A set of previews are available, for example, here, and shown below.  For more information about AVIRIS data, see this link and this link.

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The AVIRIS data portal.

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A sample AVIRIS image. 

Need access to thousands of historical aerials and topographic maps at your fingertips? Try www.historicaerials.com

April 30, 2018 3 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!

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The interface for HistoricAerials.com 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.

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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.

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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!

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Landsat 8 Image for Allahabad India on 31 May 2016.

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