Modern GIS: Imagery & Remote Sensing

BrianBaldwin · ‎07-08-2024

This is the 4th blog in a 6-part series highlighting the core concepts of a Modern GIS. To view the other blog posts – please visit this page Modern GIS Core Concepts

Over the past few years, Esri’s Education team have been discussing the technology shift and the need for GIS coursework to move from desktop-centric patterns to those that include the web. Desktop GIS is still an integral part of the story – but it is no longer the focus of the story. Desktop GIS is vital for data management, advanced analysis, and cartographic production – but many of those workflows are now part of a web-based context. Desktop tools can now seamlessly consume web-based services published by authoritative geospatial agencies and individuals across the globe. Desktop GIS can publish map services and layers to the cloud – to be consumed by web-based applications and tools, and desktop GIS can edit and manage web-based data and layers.

Through this series, we are asking: So, what does a course look like that focuses on the fundamentals of GIS but adjusts to a more web-centric paradigm?

In this blog, we will be looking at imagery & remote sensing.

Why imagery?

Isn’t GIS just supposed to be about points, lines, and polygons? Raster is faster… but vector is better? Overt language that pits one set of methods and tools (vector vs. raster) against another is long gone, but the split between these 2 fundamental ways of representing spatial information is still very real. After paging through a number of introductory GIS syllabi and introductory GIS textbooks, it’s hard not to notice this divide, or more specifically, the lack of weaving remote sensing throughout introductory GIS courses. But it doesn’t need to be this way! GIS software can visualize and analyze both raster and vector data. As well, the data coming out of remote sensing platforms have never been more detailed, timely, or interesting. When students want to solve problems related to global hunger, urban heat islands, or ecological systems, they need to leverage many data formats. Introductory GIS can focus on the power of spatial information to solve local and global problems, while Advanced GIS and Introductory Remote Sensing can be saved for wavelengths and projections.

What’s the average summer temperature in US census tracts in Milwaukee? How is this related to tree cover? How about race?

(Landsat-2 showing average surface temperature in August from 1985-2024)

Why is Russia painting jets on some of their runways? What happens when object detection tools try to identify ‘jets’ in this imagery? Where is Russia doing this?

(Image courtesy of Planet Labs)

How much erosion has occurred in the Mississippi delta over the past 40 years? What does this change look like? What communities have been most impacted by this change?

(Animation in 4-year steps, created with the Landsat Explorer showing shortwave-IR between 1984-2024 of Venice, LA)

As a 1st year student in an introductory GIS section… I don’t care what band combinations were used in the animated Landsat image! I will also probably fall asleep when we look at the chart showing wavelengths and spectrums. But – I do want to know understand why this is happening. I want to know how to measure the change. After seeing these problems coupled with tools and methods to explore them, I want to dive in deeper.

You probably don’t have a PhD in Remote Sensing (and that’s OK)

One real challenge that I think many of us face when coming from a more vector-based background, is simply the depth and breadth of remote sensing. I’ll be the first to admit that when it comes to band combinations, wavelengths, and the infrared spectrum… I sometimes find myself feeling lost out at sea. Remote sensing is an entirely different world and when we are building an introductory GIS syllabus – does it even make sense to start introducing this universe of information? Does it deserve 1-week? How about 3? Or should we just hold off and save it for the ‘imagery people’? Yet, there is so much value in using and introducing imagery/remote sensing content, especially coupled with vector data. Rather than tacking the ‘raster’ content into the 8th or 10th week, we need to reimagine how it can be weaved throughout introductory GIS. The excitement of the data products and analysis can help lead learners to further inquiry on the ‘how’ and the ‘why’. A major goal should simply be igniting that spark for how any form of spatial data can be used to help solve problems.

The ‘golden age’ of imagery & remote sensing is upon us and even in an introductory GIS course, we can’t ignore that. With cloud based parallel processing for analysis, rapidly evolving sensor technologies, and decreasing storage costs, even my 10-year-old neighbor can capture 1 CM resolution true-color imagery and build orthomosaics with their drone.

So – what are some ways that we can start introducing imagery and remote sensing in meaningful and powerful ways to learners?

Let’s Make it Easy – Esri’s Landsat Explorer

Rather than starting with downloading TIF’s, discussing image formats, and building mosaics, learners can explore decades of Landsat imagery with a simple web application: Landsat Explorer.

Simply exposing students to the history and power of remote sensing is a really easy way to get started. Also, this doesn’t need to happen during ‘Week 8’! One tool that Esri recently updated, is the web-based Landsat Explorer app, which is part of Esri’s Living Atlas. How is this imagery captured? How long has it been captured for? What is the resolution? What are the sensors? What can this imagery be used for? There is a whole range of inquiry that can be opened up with even the most basic pane on the application.

One of the locations that I was the most excited to explore when I first launched the application was the Aral Sea, located in present day Uzbekistan and Kazakhstan. In about 10 minutes, I was able to create an animation that used over 40 years of imagery to watch this once massive inland lake disappear.

(Aral Sea from 1988-2023 in 4-year steps)

Even if the application only had these exploration and discovery tools, it would be an incredibly valuable resource. But for me, the ‘Analyze’ pane really takes the application to the next level. With the provided ‘change detection’ tools, learners can select between 2 different time periods, different indices, and then build an analytic result on the fly. Rather than simply swiping between 2 different time periods, or trying to ‘see’ the change, we can compute it. I can honestly imagine this tool filling the need for a whole week of lessons and labs, but there will obviously be times when you will need to go further.

(Visualizing the Aral Sea after using the change detection tool on the water index found in the ‘Analyze’ ribbon)

Image Exploration & Analysis – ArcGIS Online Map Viewer

The Landsat Explorer application is a fantastic introductory tool to the world of imagery, renderers, sensors, resolutions, and analysis, but there will obviously be a need for learners to step outside of this curated application.

Within the ArcGIS Online Map Viewer, learners can explore many of the imagery datasets found throughout the Living Atlas and ArcGIS Online, which include Landsat, Sentinel, MODIS, NAIP, along with thousands of other imagery datasets from municipal, state, and national government agencies. Many of these datasets have pre-built renderers, include multiple years of data, can be filtered using their attributes, and can be used as the input for analysis tools.

With the latest update of ArcGIS Online – every academic user now has the ability to run raster analysis tools in the web browser. Learners can run zonal statistics, they can use hosted deep learning tools to detect objects on hosted imagery, classify pixels, and more. For advanced users, they can use or build raster templates to conduct analysis that chains tools and processes together. The ArcGIS Online Map Viewer provides all of this functionality, letting learners dive into advanced imagery and remote sensing topics without even stepping into desktop GIS.

In one simple example, we can explore the relationship between tree cover and urban heat in Milwaukee Wisconsin. Using only the ArcGIS Online Map Viewer and hosted data, we are able to filter Landsat data based on time of capture and cloud cover, and then build zonal statistics for census tracts. We can add the European Space Agency layer for 2021 land cover, showing tree cover. We can also add data related to population health, race, or ethnicity. Hosted analysis tools also provide the ability to build a composite index, which lets us combine all of these inputs based on weights and ranks that we assign. Without downloading any data or building any raster pyramids, we can explore and measure the relationship between heat, population, and tree cover. In short, we can use tools and methods that pull vector and raster data seamlessly into one workflow. A workflow that engages, excites, and encourages learners to ask ‘how’ this all works on a deeper level.

And just when they think they are safe…we hit em’ over the head with radiometric resolution in Advanced GIS or Introduction to Remote Sensing.

Next Steps

One of the ‘calls to action’ in this blog is for faculty to include imagery and remote sensing throughout introductory GIS in a more holistic way. Basically, trying to ensure that it isn’t simply tacked on as “Week 8 – Raster Data”. Using only ArcGIS Online and the applications found in the Living Atlas, you have tools and resources to do this in a meaningful way. Starting with the Landsat or Sentinel Explorer applications, learners can explore vast image catalogs and get excited about how this data can be used. As a next step, the ArcGIS Online Map Viewer, coupled with the Living Atlas datasets provide a fantastic way for students to step beyond these curated applications, and start discovering data, mashing them up, and conducting rich analysis.

Resources

The following is a small subset of resources that you can use as lessons, labs, or supplemental material for a course. Please explore any of these locations further, as there are hundreds of fantastic resources available for imagery and remote sensing throughout ArcGIS.

Modern GIS: Imagery & Remote Sensing

Why imagery?

You probably don’t have a PhD in Remote Sensing (and that’s OK)

Let’s Make it Easy – Esri’s Landsat Explorer

Image Exploration & Analysis – ArcGIS Online Map Viewer

Next Steps

Resources

Esri Academy

Esri Tutorials (Learn)

Books/Texts

Documentation/Tutorials

Other