7.4 Camera History—Concept 5
7.4.7 The “Revelle Camera”
Table 7.4-7: Important parameters of the Revelle Camera.
Original sensors JAI M4+ CL
Most recent sensors UNIQ UP-1030 with double-exposure (PIV-mode) modification
Probe volume (a) 80 mm
Distance to reference plane (L) 778.72 mm
Type of lens Achromatic doublet with 2 mm pinhole Focal length of lens (f) 50 mm
f-number of lens f/25
Aperture triangle side5 (sij) 153.98 mm
Angle of lens 6.51°
Sensitivity coefficient (B¯ij) 10.56 mm Planar resolution (R) 10.24 pixels/mm
Figure 7.4-12: 3D pinhole model of the Revelle Camera.
The Revelle Camera was the first designed by Pavel Svitek for Caltech. It was designed for use underwater behind a full-size ship, replacing the original intention of performing measurements on model ships in a tow tank (which is what the Black Camera was designed for). The goal of the experiment was to measure bubble size, population, and velocity.
Due to the size constraints, the camera was not designed as an equilateral triangle but as an isosceles one in which the blue aperture is placed half the distance from the centroid of the equilateral aperture triangle, (so its height is 2/3 that of an equilateral triangle with the same base). The
sensors were taken apart and mounted so that the chip and socket were glued to the back of the faceplate after being aligned with external stages and the bodies of the sensors were mounted on the faceplate laterally. The entire assembly had to be water-tight, so there was a lot of care (and epoxy) in the design and assembly of the lens windows and the joint between the faceplate and the
“torpedo”. Cables were run to the torpedo from the computer (atop the deck of the ship) inside of a large-diameter Tygon tube which connected to the torpedo with a custom sealing flange and hose clamps.
The stages used were the same Opto-Sigma stages used in the above cameras. During alignment for the Revelle experiment (summer of 2003), the tip-tilt stages were used. The alignment was poor and the camera was never proven to work, as the entire mast and light delivery system failed on board the ship after a swell hit the mast while it was being mounted and put a kink in it. Some of the welds on the mast were also prone to leaking.
During preparations for the Athena test (summer of 2004), the JAI sensors were replaced with the UNIQ’s from Kumar’s camera because as it turned out the JAI’s were a pair of “Revision A”
and one “Revision B” and it was impossible to synchronize them perfectly. With the UNIQ cameras the alignment was tested and the camera was shown to have a usable probe volume about 100 mm deep. However the Opto-Sigma stages have quite a bit of play, and noise in the sensors forced the use of plastic screws for attaching the sensors to the stages, thus the alignment was not perfect and pixel accuracies below 1 pixel could not be used reliably to identify triangles (using single-plane dewarping). By now the heat movement had already been discovered and thus the alignment and gluing was performed without turning the cameras off. It was discovered that the hysteresis in the sensor power-cycle movement is removed by gluing the sensors as in this camera, but the movement still exists—that is, a calibration is only valid once the sensors temperature has stabilized.
For the Athena test the mast was replaced by custom-built aluminum space frame built by Total Structures, and the setup was mounted sideways, with the camera on the port side and the illumination coming from starboard. The “laser bucket”, as the underwater housing for the laser optics was named, had several problems with leaking and the mirror was never mounted correctly so only about half the probe volume was illuminated. The laser, on loan from LaBest, suffered some damage on the first outing as it was left unrestrained on board the ship. As a result, only one laser was firing, and there were several problems with noise in the synchronization signals.
Only three runs of measurements were performed. This data was processed successfully and yielded decent sizing data, though there is potentially quite a bit of noise in the results clouding the population information for the smallest bubbles. Also several interesting phenomena were observed (namely a difference in bubble population size distribution between runs in a bay and runs in the Gulf of Mexico), but the lack of repeated runs made most of the data inconclusive.
Figure 7.4-13: The Revelle Camera (here with dummy plate) assembly just before the second leak test.
Figure 7.4-14: The Revelle Camera just prior to being mounted on the transom of the R.V. Revelle.
Figure 7.4-15: The Revelle Camera during alignment after the sensors were replaced with UNIQ UP-1030’s, seen from above the faceplate.
Figure 7.4-16:For the Revelle Camera, the chips were mounted on custom frames (unfinished aluminum) which were glued into receptacles (black-anodized aluminum) on the faceplate. This removed the hysteresis in the heat movement (though the movement had not yet been discovered at this time). Shown here is the blue sensor’s frame held in place within the receptacle by stages during alignment (top right) ready to accept the epoxy, which would fill the gap between the frame and receptacle.
The red sensor is visible on the top left, out of focus.
Figure 7.4-17: The Revelle Camera during alignment, showing the faceplate from the back.
Figure 7.4-18: The space frame, replacing the long mast from the Revelle test, mounted on the transom of the R.V. Athena.
Figure 7.4-19: CAD model of the Revelle Camera assembly for the Athena test showing the forward-scatter angle.