Comparison of land-based vs. floating calibration targets used in aerial photogrammetric measurements of whale lengths

Comparison of reproductive parameters for populations of eastern North Pacific common dolphins: Delphinus capensis and D. delphis

“…We detected a small but consistent negative bias in recorded altitude and used the regression coefficients obtained in this comparison to correct the recorded altitude for each image from which we measured dolphin lengths (Table ) (Perryman and Westlake , Mocklin et al . ). The corrected altitude was used to convert dolphin lengths measured in pixels from photographs to true dolphin length in cm for analyses.…”

Behavioral Ecology of Cetaceans: The Relationship of Body Condition with Behavior and Reproductive Success

“…Wildlife film crews are already relying to a great extent on remote-controlled aircraft to obtain footage of animals with a minimum of disturbance and future improvements in technology and reduction in costs are only likely to make such approaches more attractive. The fact that aerial photogrammetry requires photographs to be taken from straight above the animal (Perryman & Lynn 2002;Mocklin et al 2010) poses technological challenges, but gimballed systems shooting several frames a second or recording continuously using high-definition video may be able to provide useful data. However, any system will likely only ever be useable in good conditions and at wind speeds of less than 10 knots, limiting their applicability in the more exposed parts of the world's oceans.…”

“…Laser photogrammetry has been used successful on killer whales (Durban & Parsons 2006) bottlenose dolphins (Tursiops truncatus; Rowe et al 2010) and Hector's dolphins (Cephalorhynchus hectori; Webster et al 2010) Aerial photogrammetry relies on photographs of cetaceans at the water surface taken from above (usually from an airplane) at a known height. Height is usually established using a radar altimeter while some form of level ensures that the camera points straight down (Mocklin et al 2010). Because aerial photogrammetry requires use of an airplane and expensive photographic equipment, this method is comparatively costly.…”

Late Summer Distribution of Cetaceans near Barrow, Alaska: Results from Aerial Surveys Conducted During the Bowhead Whale Feeding Ecology Study, 2007–11

“…A land target was used in all years, and in 2008 and 2009, a floating water target was added to look for possible discrepancies between radar altimeter performance over land and water (Mocklin et al, 2010). Alti-tudes for photogrammetric passes were at 30.5 m (100 ft) intervals ranging from 152 m (500 ft) to 457 m (1,500 ft), weather permitting.…”

“…Measured images of the floating targets showed a strong correlation between the digital imagery and true lengths from the targets, indicating that radar altimeter performance does not change significantly whether over land or water (Mocklin et al, 2010). Of the 803 images measured for the photogrammetric length (age) class analysis, 654 were within grades 1-6 (Koski et al, 2006).…”