Researcher Uses SARscape and ENVI to Monitor Forests

Customer Challenge

Geospatial imagery provides specific information about geographic areas of interest and is used to make informed, accurate decisions in a variety of applications. One popular application for geospatial imagery is environmental conservation and resource management. Many local, national and global environmental and conservation programs have begun to take advantage of increasingly available geospatial imagery to address problems ranging from monitoring the effects of pollution to identifying optimal locations for planting trees.

In the last few decades, leaders from countries around the world started working together to tackle global environmental issues. One of the main goals is reducing greenhouse gases and ultimately, global warming. One way they are attempting to reduce emissions of greenhouse gases is from restricting deforestation and forest degradation. As countries have started working to mitigate global warming, they have struggled with the complexity of measuring and monitoring their diverse ecosystems and land use changes, which is essential to determining if efforts are achieving positive results.

Solution Achieved

In order to address the challenge of measuring and monitoring ecosystems and land use changes, the Group on Earth Observation (GEO) Forest Carbon Tracking Task (FCT) was established and has become a partnership among close to 80 governments and 56 leading international organizations. The aim of GEO FCT is to demonstrate the feasibility of coordinated Earth observation to monitor forests and collect information to serve as input to future national forest and carbon monitoring systems.

Dr. Anthea Mitchell, Visiting Research Fellow in the Cooperative Research Centre for Spatial Information based at the University of New South Wales, is one of several individuals around the world tasked by GEO FCT with creating standardized methods for processing data and imagery and generating forest information products for use in carbon assessment. Ultimately, Dr. Mitchell is working to develop image analysis routines that can be used worldwide to measure, monitor and report forest change.

One of Dr. Mitchell’s primary methods for monitoring forest change is using important data from both optical and Synthetic Aperture Radar (SAR) imagery. The differences between these types of imagery make them a great complement to each other. SAR sensors emit their own illumination source in the form of microwaves, which allow them to record data at all times of day and not just when the sun is shining. SAR uses different wavelengths than optical sensors, allowing it to record data through atmospheric interference like clouds and storms. These wavelengths combined with the fact that SAR is a side-looking sensor, compared to optical sensors that mainly look straight down, mean that terrain and cultural targets respond uniquely to radar.

Since SAR scans the Earth differently than optical sensors, it is giving Dr. Mitchell a unique layer of contextual information about specific geographic areas of interest. “SAR is unique in that is provides information about 3-dimensional structure and moisture content of items on the Earth’s surface and is very useful for discriminating and mapping different forest types and biomass.”

In order to effectively use the SAR data Dr. Mitchell is given as part of GEO FCT, she needed a solution that could effectively process and analyze SAR data and easily work with optical imagery. After evaluating her options, she ultimately chose SARscape® Modules for ENVI. SARscape has unique capabilities to read, process, analyze and output information from SAR data and imagery. SARscape converts data from hard-to-interpret numbers to meaningful, contextual information. And, because SARscape is integrated with ENVI, a widely used image processing and analysis solution, users can take advantage of multiple types of imagery and exploit the critical information they contain.

To extract valuable information within SAR data, it must first be read and processed. Since Dr. Mitchell is given SAR data from a variety of sources, such as ALOS PALSAR data from the Japanese Space Agency and RADARSAT-2 data from the Canadian Space Agency, it is critical that she has one software package that can accurately read the data in the correct format. “SARscape streamlines the process of importing SAR data from a variety of sensors and accurately reads it in the correct format,” says Dr. Mitchell.

After reading the SAR data, Dr. Mitchell uses SARscape to quickly and easily perform a variety of automated processing tasks to prepare it for visualization and analysis. These processing tasks include multilooking, coregistration, despeckling, geocoding and radiometric calibration, and mosaicking. Since radar images typically have a lot of noise, Dr. Mitchell thoroughly filters them to minimize the noise. The coregistration process automatically superimposes images acquired over the same area on different dates. The data is also geometrically and radiometrically corrected, which is required to be able to analyze and compare images acquired at different times or by different sensors.

“SARscape is one of the only complete packages out there that can do the whole suite of processing to bring our data up to the level of a geometrically corrected and properly calibrated mosaic,” says Dr. Mitchell. “The flexibility of the tools in SARscape also means we maintain the integrity of our data during processing, which is a must in order for us to accurately analyze it.”

After processing the SAR data, Dr. Mitchell analyzes it using ENVI. Because SARscape is integrated with ENVI, she can perform advanced image analyses without leaving the software. The change detection tool in ENVI is used by Dr. Mitchell to detect and measure changes between the images. The automated workflow for detecting change in ENVI identifies the type and extent of changes that have taken place in an area over time. Using change detection, Dr. Mitchell looks for increases and decreases in brightness which often signifies forest areas that have been cleared or that have regenerated. Because an increase in brightness might also be a result of an increase in soil or canopy moisture, optical imagery is brought in to confirm the results.

“The change detection tool in ENVI is fantastic for finding and identifying changes that have occurred over time,” says Dr. Mitchell. “And, the fact that SARscape is part of ENVI means that we have access to all of the tools within ENVI which is very useful when it comes time to analyze and interpret our data. The many spectral tools for example, allow us to explore the unique radar signatures for different forests and cover types, which greatly assists when it comes to classifying the data.”

Dr. Mitchell has had a lot of success achieving the objectives she was tasked with as part of GEO FCT. She has been able to generate annual forest and non-forest extent and land cover maps and change maps that show deforestation and regeneration changes over time by processing and analyzing SAR and optical imagery in SARscape and ENVI. She has created standardized methods for processing and analyzing SAR data from different sensors and used it to create forest information products for carbon assessment. “SAR data has provided us with critical information that we wouldn’t be able to gather solely using optical imagery. SARscape and ENVI have enabled us to quickly and accurately process and analyze our SAR data. We couldn’t complete the work we have done without this software package,” says Dr. Mitchell.

Key Benefits

• Using SARscape, Dr. Mitchell is able to easily input SAR data from a variety of sensors and accurately read, process, analyze and output information from it.

• Since SARscape is integrated with ENVI, Dr. Mitchell can quickly and efficiently perform advanced image analyses without needing to switch between multiple software packages.

• Dr. Mitchell can combine SAR data with optical imagery in ENVI to add additional layers of contextual information about geographic areas of interest.

For more information on GEO FCT, go to http://www.geo-fct.org. For more information on SARscape® Modules for ENVI, go to www.nv5geospatialsoftware.com/Products/ENVI-SARscape.

Acknowledgements

Group on Earth Observation (GEO) Forest Carbon Tracking Task (FCT) International Forest Carbon Initiative (IFCI) - Research Alliance (RA) School of Biological, Earth & Environmental Sciences, University of New South Wales sarmap SA team