Photogrammetry in the Forest: Digital Photogrammetry Improves Forestry Data Management and Analysis
Finding a rational, balanced approach to managing the world's forests begins with accurate,
current information on forest conditions.
By J.D. Wilson

As forest resources become more scarce, environmental regulations more strict and public scrutiny more intense both public and private forest managers are looking to a new generation of GeoTechnologies to help them better understand and manage the resources in their charge.
      Integration of aerial photography and satellite imaging, along with Global Positioning Systems (GPS) and sophisticated geographic information systems (GIS), into a cohesive environment is increasing the professional forester's ability to collect and analyze diverse and complicated information regarding forest ecosystems.
      "We're not just looking at trees, but how to manage entire ecosystems," says Stan Bain, operations program leader, Remote Sensing Applications Center of the U.S. Forest Service.
      He explained that ecosystem management expands the need to monitor and analyze changes over time. It encompasses all the variables in an area, including drainage, watershed, vegetation, habitats, fisheries, wildlife biology, and ownership records and political boundaries.
      Bain sees a growing need for sophisticated information management systems as the foresters' job gets more complex. In many ways, foresters must also be skilled information managers. Moreover, Bain stresses the need to be able to exchange data between various government agencies and private landowners. "Ecosystems don't recognize political boundaries," he said.
      Building on a legacy of information created from aerial photographs and field expeditions, today's foresters are building comprehensive automated information systems. "Remote sensing provides a look at the big picture that cannot be achieved by manual means," Bain said.

From Photos to GIS
For more than 60 years foresters have worked from analog orthophotos and for the large part this is still the industry standard. Multiple copies of the photos are printed and distributed to planners and field crews, who use them alongside traditional paper maps.
      But now they are finding they can take a digital version and use it as a backdrop in their GIS, combining photo images with their digital base maps.
      "Aerial photography has been used since the 1930s and it's still the backbone of remote sensing," Bain said. While he sees benefits in many interesting newer technologies, including videography and radar applications, he said computer enhancements have had the most impact on their operations.
      "Digital photogrammetry can really speed up the analysis," Bain said. "You start with a digital format that you can port directly to your GIS."
      With the added ability to integrate raster images, its efficacy in the forest has increased exponentially. "Now they can have a true image backdrop to fill in the information," explained Ward Carson, professor of Forestry and GIS at Oregon State University, Corvallis, Ore. "Orthophotos are a more complete source of information than you can compile in a vector-based GIS."
      Carson pointed to newer integrated systems, which offer the ability to incorporate an image as a backdrop in the data collection phase. "We can use these systems in the task of making a new map as well as in analyses."
      He explained that photos can be used to identify and analyze forest types, cut units, stand ages, streams, roads, ownership borders, and may other features.
      "We can use this information in constructing roads, logging, replanting harvested areas, and managing pest or fungus infestation," he said. "These features were really available in previous instruments, but using them was more complicated given foresters' resources."

The Ultimate Map
"We are always trying to create the ultimate map that can save us money," said Simon Lanoix, who coordinates digital mapping operations at McMillan Blodell in British Columbia. "Photogrammetry is clearly the best way to develop this map. We have not found a better way."
      The better the map product, the more efficient your planning and operations; and, said Lanoix, "The better the map, the less field work is required." Deploying its field crews for maximum value is a high priority for McMillan Blodell. Anything that can be done in the office frees a crew to perform more critical or more complex functions.
      The firm has developed a corporate inventory base to support planning of its logging activities. A reliable inventory of existing stands of timber and growth is important in quantifying and qualifying the value of that inventory for future activity.
      Lanoix uses that data to plan future cut blocks, decide where to build roads, schedule field work and perform post-harvesting regeneration planning.
      He stressed the need for reliable information in planning, maintaining its inventory base and keeping up with regulatory compliance. "We're very concerned about visual impact assessments," he said. Canadian regulations now include a consideration of how cutting in one area will affect the view for hikers and tourists in surrounding areas.
      "Regulations now include a visual impact objective," he said. "This is the back yard of Canada. It's a high tourist area."
      Whether it's environmental impact reports for new cut blocks or transport plans through wilderness areas, foresters are faced with mounting regulations, and a sometimes hostile approval process.
      "To get their plans approved, they have found that graphics are more effective than verbiage," explained George Southard, sales manager for Leica Americas, Englewood, Colo. "It helps people understand exactly what they are planning and can speed along the approval process."
      "The thing I hear most often is that foresters need higher quality maps and they want them faster," Southard said. "Everyone is looking for ways to create better low cost maps that can support detailed planning."

Bridging Photos and Maps
Traditional interest in ortho photography by foresters emerged out of frustration with the displacement images in aerial photos, according to OSU's Carson. "If you take a photo over a hilly forested area, the photo is not a map. Images are displaced proportional to shape of ground," he said.
      "Aerial photos have been the main medium for keeping track of forest resources and navigating through a large area," Carson said. "But a photo is not a map unless it is transformed, so most recent technology which can transform photos and maintain resolution, is very interesting to foresters.
      "Photogrammetry's gift is to present a photo without displacement. The photo image can have the same accuracy as a map," he added.
      Carson likes what he sees in the new generation of soft copy photogrammetry systems. "In past photogrammetry systems have been expensive and there was always some quality loss in the resolution of images," he said. "In the digital domain, orthophotos are cheaper and original resolution can be maintained in the ortho product."
      He says the real advantage is the ability to achieve higher quality at cheaper costs thanks to computers. "Foresters have always been a major consumer of orthophotography. They use lots of photos," he said. "Now, convenient images are getting more accessible. There's nothing quite so powerful or easy to understand as a picture."
      Carson outlines four main advantages to digital orthophoto systems:
      1. Cost control. A digital environment helps make information more manageable and accessible to end-users. Carson explained that a typical forestry operation would capture resource photos every other year. The Weyerhauser region in Oregon, for example, covers 500,000 acres. At a 1:12,000 scale, they collect and process as many as 3,000 to 4,000 photos every other year. Then, compound that number tenfold for getting copies and handing them out to engineers working in the field. By simplifying the data collection and processing requirements of creating digital ortho photos, softcopy systems can save both time and money for high-volume users.
      2. Automatic features. Carson sees a lot of promise in the automated features provided by digital systems. For example, "the ability to pull out an automatic DEM to describe your ownership more completely, is a real attraction to foresters," Carson said. "Earlier maps were planimetric with implied z coordinates by contour line," Carson said. "In a digital system, a DEM is a more convenient representation of x, y and z. New photogrammetric instruments can derive a DEM more easily, automatically." He explained that trees grow differently on a southern slope than a northern aspect, with harvesting and road construction more difficult on steep slopes. "A DEM gives you slope and aspect attributes that enable you to prepare for these challenges."
      3. Advanced Analysis. With digital systems, Carson said, it will be possible to process detailed information, such as stems per acre (stocking assessment), size of trees (height) and diameter (correlates to height).
      "You can take a little closer look at your assets - track inventory," Carson said. "I've been working on using auto terrain extraction to get a DEM of bare ground, and then take a later photo and do a DEM over the forest canopy. By subtracting the bare ground DEM from the canopy, we can determine the volume of a forested area."
      With robust, automated analysis capabilities, he sees these new-generation systems playing an important role in tracking inventory and monitoring growth of forests. "We can quantify early indicators of problem areas," he said. "It will enable us to determine if and where a forest is not growing as well as it should and identify health or pest problems."
      4. Support for Sophisticated Planning. As forestry becomes more refined many larger operators are actually trying to apply just-in-time delivery concepts to forestry. With a 30 year rotation for forests and planning operation on a larger scale, proper long-term management is essential to a successful operation.
      "If you know a ship will be at a certain port to be loaded with a certain product at a certain time, forest harvesting can be scheduled so logs would be delivered on time to that dock," Carson said. "These are the kind of thoughts that are in the air now."
      "A more refined inventory based on high resolution DEMs can get much closer to a JIT-type operation," Carson declared. "It can be very useful in shipping and local milling operations, as well as long-term harvesting and revegetation projects."

High End Systems
While softcopy photogrammetry is still a generation or two from the desktop, the barriers to entry are falling. With training and software, a softcopy system typically costs about 25 percent less than a comparable hardcopy system. "It's a more automated process," said Leica's Southard. "You don't need point transfer devices, off-line triangulation software or some of the other peripheral devices necessary for traditional photogrammetry."
      Compared to the manual analytical stereoplotter, however, softcopy systems are easier in terms of operator training. "You need fairly good knowledge of the mapping business generally, but don't have to be photogrmmetrists or have skills of stereoplotter operator," Southard said. "You need some basic computer skills and knowledge of UNIX. It opens up the number of people able to use it."
      Southard cautions that softcopy systems should not be looked at as a replacement for existing systems. "They both have their strengths. They can be very powerful together," he said. "The biggest thing for digital photogrammetry is the flexibility it offers the customer, particularly if they are adding it to a shop with hard copy capabilities."

Enhanced Productivity and Visualization
Finally, Southard pointed out that while softcopy photogrammetry is more affordable than traditional hardcopy systems, the major advantage is in higher productivity or the option of bringing mapping and analysis in-house and contracting less out.
      "The best advantage of softcopy systems lies in time and productivity," he said, "and the ability to create orthophotos and perspective scenes," Southard said. Digital systems have led to a fly-through capability, which enables users to present a three-dimensional view of an area from virtually any vantage point.
      An orthophoto shows a bird's eye view. But this is sometimes difficult to interpret, especially for non-technical people who may be involved in the decision-making process.
      "All of us look at the world horizontally. Only a few of us have the opportunity to look at the world vertically," Southard explained. "If you present information in a horizontal perspective, the general public can understand what you're showing right away."
      With the current tug-of-war on the world's forests, understanding is a very valuable commodity.

About the Author:
J.D. Wilson is a freelance writer and industry analyst in Aurora, Colo. He reports on technology in business, especially the GeoTechnologies, and maybe reached at 303-751-0755.

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