Archive for August 2013
Several developments in data accessibility and technology have helped launch a popular revolution in the use of remote sensing technology. The Landsat program run by NASA and the USGS has had a series of satellites orbing the earth since 1973 and has recently put its entire 40-year archive in the public domain. What this means is that students, teachers, scientists and citizens can now access detailed imagery of anywhere in the world to analyze vegetation, land cover and change. This has interesting implications for teachers and students in the International Baccalaureate Diploma program.
Remote Sensing (RS) and Geographic Information Systems (GIS) is not formally a part of any IB Diploma subjects. Anyone pursuing geography at the tertiary level will have to have GIS skills, but this has not been incorporated into the teaching requirements. The Geography, Environmental Systems & Societies and Physics courses, all have opportunities to use these technologies to address key concepts and learning outcomes. In DP Geography GIS is a useful tool in building geography skills (core 1.0) and the Urban Environments option. I teach basic GIS skills to all of our Geography students for them to use in the Internal Assessment as well as areas of the core syllabus (populations in transition etc.). We are also working in the OSC Humanities department to introduce basic GIS mapping skills at an early age. Despite GIS & RS only playing a minor role in the syllabus, they are showing up in final assessments. The May 2012 IBDP Geography exam question, for example, featured a Landsat image of urban growth and sprawl in the Pearl River delta taken from the NASA Earth Observatory.
This year we have acquired two Vernier ALTA II Reflectance Spectrometers. I was exposed to the use of these while at the JOSTI workshops at Thomas Jefferson School for Science & Technology last summer. A highlight for me -and I was the only participant – was taking the Remote Sensing workshop with Lisa Wu and Shawn Stickler. They run courses in Geosystems and Oceanography which both utilize GIS and RS applications. Students at TJ are actively involved in the design and usage of their data gathering equipment. One of them had completed impressive work in the Chesapeake Bay interpreting temporal data using Landsat images combined with ground truthing trips.
The Alta II meters are relatively simple gadgets that measure the reflectance of different colors from a given surface. The meter operates by shining a small LED light (from Deep Blue up to Deep Red and Infrared). A photo sensor records the amount of light bouncing back into the meter. The value that the meter gives is then divided by the particular color’s wavelength (in nm) minus the “dark value” (value of meter when no color buttons are pushed). So it does take some simple division to actually arrive at the reflectance percentage once you have your readings. These can be graphed (see jack example blow) and then compared to standard values. I ran an initial trial using mango (Mangifera zeylanica) and jack (Artocarpus heterophyllus) tree leaves. The next week our Grade 12 students conducted a similar test on a variety of surfaces as a part of their IB Group IV project. Reflectance is quite consistent for various species but there would be variations based on the age of leaf (which is why I took values for two different jack tree leaves). NASA has a helpful online spectral calculator for looking at reflectance values of different species in North America.
What is interesting is to use the reflectance meter to corroborate or ground truth reflectance values of surfaces that are visible in the Landsat satellite imagery. The normalized differential vegetation index (NDVI) has also become a standard test run using RS images. It measures a value of vegetation in a given area and this can then be compared to the same area at other times. The Earth Observatory has a clear explanation of the NDVI index. India’s Aligarh Muslim University also has an excellent article on reflectance that is worth looking up. In the coming months my students and I will be working to make clear linkages between Landsat imagery and the values that they are collecting in our area.
If you are looking to access the Landsat Program the best point to start is the USGS Earth Explorer (this is better achieved using a browser enabled with Java). Earth Explorer has a wide range of spatial data available and it is worth exploring all the many different data sets. Another point to access basic spatial data from Landsat (without having to process it) is the Terralook site. You can also use the Glovis Site (that I had recommended in my post a year ago). When I am working with Landsat data I download full GeoTif files from Earth Explorer and then work with the different tiles using ArcCatalog and ArcView (Desktop). Having a fast Internet connection is essential for this. I have started a page on my Mango Wiki site to help my students access Landsat data and instructions that are available online. A very useful manual to have is Remote Sensing for Ecology and Conservation authored by Ned Horning and several others at the Center for Biodiversity & Conservation at the American Museum of Natural History. For a portfolio of images taken from space and clear explanation of the way satellites gather multi spectral data see Andrew Johnston’s Earth From Space (Smithsonian National Air and Space Museum, 2007). The Alta II reflectance spectrometer meter is available through Vernier in the US and comes with a manual of lessons plans. It does not plug into the Lab Quest devices that most science labs are using.
Over the last year I have continued to work with various methods of presenting elevation for the study areas that I am interested in, both for school (here in Sri Lanka) and for personal work (in India’s Western Ghats). The two maps here are the result of experiments with hypsometric tints. This method uses contours lines derived from SRTM Digital Elevation Models (DEMs) and assigned colors bands to present variation in the topography of the land. As my ongoing photographic documentation and writing of the Western Ghats illustrates, I have a multi nodal interest in the landscapes, ecosystems and cultures of the region. These experiments with maps are part of my ongoing efforts to better understand, document and share information on this stunning yet threatened South Asian landscape.
For further information on cartography using GIS see the excellent site Cartotalk. The Cartography and Geographic Information Society promotes a wide range of geographic skills with plenty of GIS links. ESRI promotes the art and science of map making using its propriety and online software through its mapping center. There are also several books out that are helpful , although with the rapid change in technological development some of these books quickly go out of date. One book that I got several years ago is Gretchen N. Peterson’s GIS Cartography (CRC Press, 2009) and as mentioned on a previous post Map Use. 6th Edition (John Kemerling et al. 2010, ESRI Press) is a must have resource for understanding maps.