EVS :: Erdman Video Systems

Coastal and Shoreline Monitoring

Coastal and shoreline monitoring using remote visual instruments has recently become more common as inexpensive high quality imaging products and computers have become available. For acquiring data, video cameras are used more than any other imaging device, and have been readily available for more than 30 years, however digital cameras have entered the monitoring and documentation systems more recently. There are advantages and disadvantages to both types of systems and these systems become more useful when they are coupled with the Internet for real time publishing of images, automated reports, and for maintaining an online archive. Below we will explain several procedures that are routine to Coastal monitoring including several concepts pioneered by Erdman Video Systems:

A. Why do Coastal and Shoreline Monitoring?
B. What equipment and services are needed?
C. Analog versus Digital cameras
D. Image Averaging
E. Noise and JPEG Compression
F. Getting useful information from the images
G. Tools to study the images
H. Online archiving of the images

I. Acquisition and Processing tools for average, variance and time stack images

Why do Coastal and Shoreline Monitoring?:

Coastal communities often have significant economic activities centered around the coastal zone; tourism, commercial and sport fishing, shipping, and boating being the main activities. The private, commercial and public lands on the coast are overseen by local communities, and many issues such as taxes, tourism promotion, construction permits, land development, and even financial compensation for storm damaged properties are handled by the local governments. Keeping track of the various activities along the coast can be expensive, and often long term documentation of the coast zone is simply not done because of cost considerations.

Imaging the coastal regions with video and digital cameras can help in the documentation of the coastal zone, and can provide a very cost effective way to:

A. Document public works such as beach nourishment and construction projects
B. Offer the public a real time view of project activities
C. Document shoreline changes (areas of erosion and accretion)
D. Identify "hot spots" and track them (Timestack)
E. Monitor and document marine traffic
F. Beach usage
G. Obtain a long term overview air quality conditions such as haze and smog
H. View surface water conditions such as storm runoff, sewage discharges, surface slicks ( river discharge)
I. Turbidity studies
J. Tourism promotion and show local weather conditions

What Equipment and Services are needed?:

The main components of a Coastal Monitoring system are:

A. The imaging device (video and/or digital camera)
B. A computer and software to control the imaging and uploading activities
C. An internet connection (telephone line, satellite connection, LAN, etc.)
D. Power (grid power, solar, batteries, etc.)
E. An FTP site and Web site to receive and present the data and images

Analog versus Digital cameras:

Video Cameras have an analog output which gets digitized by a video digitizing board and produces images with resolution up to 640X480 pixels using a typical NTSC video signal. Images can be captured as fast as 30 frames (60 fields) per second. When compressed, single video images typically have files sizes from 30K - 80K bytes. A 3.1 megapixel digital camera produces images directly in digital form, with resolution up to 2160X1440, and can acquire images at a rate of one image every 10 seconds and when compressed, single video images typical have files sizes from 300K - 1000K bytes.

The images below illustrate the differences between a typical frame of video and a typical digital image. Note: the digital image size has been cropped to 640x480 region to fit these pages, it's original size is 1536x2048:

Image Averaging:

Averaged images are acquired by using neutral density filters and long exposure settings. With the appropriate filters, exposures up to 16 seconds can be taken producing a truly average image. Multiple long exposure shots can be averaged together. In practice, the multiple images are 1 minute apart, and each image represents a 16 second average, so in 10 minutes, a "160 second average" image can be acquired. This is one of the image processing techniques that reveal features the eye does not pick out easily. Image averaging of the shore area is usually done in 5-10 minutes segments with the averaging done on a pixel by pixel basis. Areas of the image that don't change over the averaging time end up looking just like a good photo, whereas areas that change (like people moving or waves breaking) get washed out and only the average color is retained for those areas. Often images are converted to gray scale so numbers can be manipulated more easily, but retaining color generally reveals more information such as small changes in turbidity that can get lost with the removal of color information. Examination of the images below will demonstrate this effect:

Averaged images help in the following ways:

A. Identification of the shoreline
B. Location of sandbars and areas of rip currents
C. Changes in water depth near the shoreline

The resulting images using this approach depend strongly on the tides and the waves. If there are no waves, one cannot see the "breaking wave" signature of the sand bars and other shallow features.

Averaged images also reduce the noise level and bring out small changes in color that the eye can see but video and digital cameras often miss. This includes seeing through the water to the sand bars and seeing differences in water masses that have slightly different color. Surface slicks are also enhanced by image averaging since the sea surface reflections tend to get averaged out.

Noise and JPEG Compression:

Examine the test image below that was taken in low light conditions.

Notice the blown-up image on the left contains varying intensity points containing sensor noise whereas the vertical and horizontal 'line-like' features are artifacts of JPEG compression. The blown-up image to the right is the result of 20 averaged images where you will notice that noise levels are much lower. Not only is the image quality increased by applying an averaging filter, but compression levels are also increased. Compressing the noise is costly, and it makes sense that the averaged images are compressed to a smaller size for the same quality by removing the normally associated noise. Reductions in file size from 30-50% is common utilizing this technique.

Getting useful information from the images:

Quantitative information that can be extracted from the imagery include:

A. Width of the beach at a point and its time evolution.
B. Location of erosion/accretion points.
C. Coordinates of the shoreline.
D. Location of erosion/accretion time history.
E. Conditions associated with erosion events.

Perhaps the most sought after information is the changing width of the beach best facilitated with averaged images. Movies are a convenient way to get an overview of what the image set looks like. An even better solution is a movie/slideshow written in Java for the Internet.

Tools to study the images:

When dealing with images from a camera that contains three degrees of motion (Pan, Tilt, Zoom) one must design high precision position devices with post processing software correction tools to maintain a high degree of accuracy over time. Using a pan/tilt unit to position the camera for shooting different scenes has the clear advantage of covering a much larger area than with a fixed camera, but also introduces some complications in comparing images. The main problem is that the pan/tilt has limited precision and therefore the alignment of each image can be slightly different. Security system have a typical accuracy of 1 degree whereas the system we use has a precision of about 0.1 degree. Even with this higher degree of accuracy, the images can jump around quite a bit, especially at increased zoom levels.

Picture Alignment: For some purposes, no correction is necessary, but in others, it is necessary. This can be accomplished laboriously with off the shelf graphics program but customized software can speed the job up enormously. Can this be done automatically? Sometimes, if the lighting conditions are consistent enough, this is possible, although all results need to be checked. Doing this one image at a time can go quickly if there is a reference point in the image. A data set of these offsets can be saved so the job only has to be done one time. 10-15 images can be done per minute; data sets with 1 thousand images can take 1-2 hours.

Rectification and Stretching: An overhead view of the coastal zone often makes viewing the imagery easier. Done properly, one can assign world coordinates to locations within the images. Sometimes, its more useful, and much quicker, to simply stretch the image in a linear fashion and calibrate the region of interest using a few field measurements. An Example from a current camera system in the field. The camera is located at SantaGiulia above Cavi, Italy.

The wide panorama shot:

The zoomed panorama shot:

A particular area of interest is the shoreline around the pennelli:

Zoom on the pennello:

stretching the image gives:

A summary of many months of monitoring can be presented like this to study the day to day evolution of the shoreline.

Event Cataloging and Analysis:

A significant turbidity event captured July 17 2001. These events can be captured and cataloged for later study which provide insight into coastal dynamics. Wind and weather conditions can also be plotted to help correlate atmospheric conditions and their effect during these events.

Online archiving of the images:

Online archiving of relative data provides instant access to images for analysis and data management. Sharing content and imagery from the system is made easy using the internet. Many interested groups can access this data simultaneously 24 hours a day. There are numerous benefits including:

A. On line archive so everyone has access to all the imagery.
B. Summary pages of key events.
C. Cost and maintenance sharing to reduce overhead.
D. Alignment and rectification of selected imagery with scale.
E. Uploading to the Internet for near real time assessment to multiple clients.