From 1998 through 2004 video data was taken using a Sony DCR-TRV900 Mini DV camcorder enclosed in an Amphibico VHDB0900 Dive Buddy Housing. During early 2000 we added a Quest Aqua-Lite dual head U/W video light system later updating to NiteRider divelights.
Will Smith of the UH Dept. of Geography running a video transect. Photo by Paul Jokiel.
CRAMP has since improved its methodology to keep up with advances in technology by replacing video with digital stills. Unlike prior digital cameras, recent cameras have resolution superior to video and the card media can store close to 1,000 high quality images. The initial costs of the equipment are lower and the images can be archived. The valuable in situ time is shorter as well as the time spent processing the images. Frame-grabbing is completely eliminated. A monopod assures a constant distance from the substrate. This monopod holds the camera completely vertical so there are no oblique angles. Prior to the switch, the compatibility of the methods was assessed through intercalibration, using both methods (video and digital still images) at a large number of sites (30) that encompassed a wide range of coral cover. Once the methods proved compatible, all subsequent surveys were conducted with digital cameras. Since 2004 high resolution digital images are taken along a 10 m transect using an Olympus 5050 zoom digital camera with an Olympus PT050 underwater housing. NiteRider underwater dive lights are mounted to a cross piece to provide consistent lighting at depths deeper than 5 m or in conditions with poor visibility. The camera is mounted to an aluminum monopod frame, 1.7 m from the substrate to provide a 50x69 cm image. A 6 cm bar provides a measurement scale.
Kuulei Rodgers running a digital monopod survey. Photo by Paul Jokiel.
The photographer follows the following procedure:
Both landmarks and GPS are used to relocate a site. In many cases the use of landmarks is faster and more convenient than using the GPS position to relocate the transect site. The diver proceeds to the start of the first 10 m transect and photographs the transect number on the clip used to mark the site. These clips have been placed by another diver laying out the transects. Hand signals in front of the camera (number of fingers representing transect number as used in American sign language) are also used to avoid any confusion during analysis. The photographer then takes 20 non-overlapping images along each 10 m transect. Each of the 10 transects along the 100 m spine line is recorded in this manner.
Laboratory Data Analysis
The software program PhotoGrid is used to quantify percent cover, richness and diversity of corals, algal functional groups and substrate cover. Images are downloaded and the 20 non-overlapping images from each 10 m transect are imported into PhotoGrid where 50 randomly selected points are projected onto each image for a total of 1,000 points per transect. These data are saved in a comma separated values (CSV) file, proofread in Excel and imported into Microsoft Access XP, a relational database. Access data can then be queried and exported to statistical programs for analyses. The statistical data analysis includes a repeated measures ANOVA design with nesting of transects in depth where frames per transect are treated as sub-samples along a transect.
This example of the PhotoGrid screen shows the 2 components for the data analysis. On the bottom are the identifying codes for the Hawai‘i version of this software. It is divided up into coral species and non-coral substrate types. The individual doing the analysis goes through the 50 randomly generated points on the image to the right and identifies the coral or substrate type under each intersection. These values are then recorded on the list in the left portion of the screen and later written to a file. (Click for a larger view)
|Photoquadrats -- Digital Camera Transects -- Rugosity Measurements -- Sediment Analysis|
Last Update: 04/21/2008
By: Lea Hollingsworth
Hawai‘i Coral Reef Assessment & Monitoring Program
Hawai‘i Institute of Marine Biology
P.O. Box 1346
Kāne‘ohe, HI 96744