Time-Series Photographs

Instrumentation Time-series bottom photographs were obtained at site C by means of a Benthos 35 mm camera mounted on the tripod frame (figure 4). The camera was mounted about 0.6 m above the sea floor and aimed downwards; a strobe illuminated the sea floor from one side of the image. The field of view of the camera is 54 degrees, resulting in an image area measuring approximately 0.6 m by 0.4 m. Instrumentation mounted on the same tripod frame measured temperature, light transmission, conductivity, and pressure every minute. An upward looking ADCP measured current; the first measurement bin is located at about 6 m above bottom.

The following figure is in PDF format. Figure 4.

The images were taken on Kodak Ektachrome Professional Transparency Film (E200) (100 foot roll, about 700 images/roll). The Benthos camera places the images in a non-standard format along the long-axis of the film (this allows a larger image size of the bottom than if the image were placed across the film in a standard 35 mm format). The film is advanced using an O-ring drive; the loose drive and drive-motor inertia results in the distance between frames varying slightly with each image.

The camera and strobe were controlled by a timer set to obtain an image every hour. The time of each photograph differs from a uniform spacing by a few minutes because of drift in this analog controller. A digital LED clock, separate from the controller, placed the hour, minute, second and day on each image. The day counter counts to 31 and then rolls back to 1.

Movie creation

Time-lapse movies were created from the individual bottom photographs. Each image on the 35 mm film was digitized as a .tiff image at a resolution of 4238 by 2626 pixels by Amaranth Photo Imaging. The exposure was kept constant for all frames, so that changes in light intensity reflect changes in water clarity, instrument fouling, and/or ambient light. The images were reduced to 600 by 372 pixels using PolyView (www.polybytes.com/); this image size was chosen to balance resolution and publication size. The camera controller was set to obtain an image every hour. However, this controller (separate from the digital LED clock that placed a time on the images) drifts by a few minutes over the course of the deployment. For the purposes of the movie, the images were distributed at an even interval between the start and stop time of the photographic record, as determined from the LED clock. The camera controller occasionally missed an image or exposed multiple frames; missed images were filled with blanks and multiple images deleted. MATLAB software (www.mathworks.com) was used to align the images, make the data plots, and create the .avi movie.

Description of movie frames

Each movie frame includes an image of the sea floor at the top and shows oceanographic data collected at the same time at the bottom. The movie plays at 3 frames/second or 8 seconds/day. The field of view of the image is approximately 0.6 m wide and 0.4 m high. The white arrow in the upper left of the frame points toward true north. The file name of the image is in the upper left corner of each frame (this number provides a key to the individual .jpg images, see ‘Images’ in the table below). The red digits in the lower left corner of the image show time (in Eastern Standard Time): HR.MM (hour and minute) on the upper line and SS.DD (second and day) on the second line. The day (DD) counter rolls over every 31 days and thus does not indicate true day of month for the entire deployment; the correct day of the month is below the data panel (see below). The third line of red digits is a record identifier NN (the last two digits of the USGS mooring number).

Below the image to the right is a data panel that shows a plot of: current speed (in cm/s) at 6 meters above bottom (mab) (in red); beam attenuation (in m^-1), a measure of water clarity, at about 0.5 mab (in blue); standard deviation of bottom pressure (in mb), a measure of wave intensity, at about 1.1 mab (in black); and water temperature (in degrees C), at about 0.5 mab (in green) obtained every 60 seconds. The values of current speed, beam attenuation, standard deviation of pressure, and bottom temperature at the time of the photograph are also listed in the data panel. The vertical black line in the center of the data panel is the time of the photograph. The plot shows four days of data, two before and two after the image displayed was obtained. Below the image to the left is a vector plot showing current speed (length of line) and direction toward which the current flows (true north is up in this display).

The time below the data panel is the time for each image (in Greenwich Mean Time), computed by evenly spacing the images over the deployment (these times are in table framelist535). The best estimate of the time of the image is obtained from the hour and minute recorded by the digital clock on the image (in EST), and the day from the data panel.

Play movies and view images

The movie of time-series photographs may be viewed using an image viewer such as Quicktime or Windows Media Player. Click on Movie in the table below to open the movie, or navigate to the file on the DVD-ROM (in the sub-directory TRIPOD535) and open with an image viewer. Click on Images to open thumbnails of individual images; click on an image to view the image at a resolution of 600x372 pixels. Each set of images contains several hundred images and may take a few minutes to open. Image times are in an table (framelist535)

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