NARWC STRIP right-angle distance code books — narwc_strip

STRIP encodes the right-angle distance of a sighting from the track-line as an interval, not a point. Two different code books are in use, and which applies depends on the survey programme, the date, and the aircraft.

Usage

narwc_strip_bins(
  scheme = c("cetap", "nlpsc"),
  platform = c("skymaster", "at-11"),
  units = c("m", "km", "nmi")
)

Arguments

scheme: "cetap" or "nlpsc".
platform: "skymaster" or "at-11". Only affects the "cetap" scheme, where the bins above 1 nmi differ by aircraft.
units: "m" (default), "km", or "nmi".

Value

A tibble with code, side, distbegin, distend.

The two schemes

"cetap": The original scheme (handbook 8.A.31). Codes 1,2 cover 0-1/4 nmi; that closest interval was subsequently split at 1/8 nmi, giving 3,4 and 5,6. Both forms occur in the archive, so 1,2 is kept as the wider unsplit bin rather than being silently merged. Intervals beyond 1 nmi differ by aircraft: the AT-11 has a single open bin above 1 nmi, the Skymaster splits at 2 nmi.
"nlpsc": Defined for the NLPSC / Massachusetts CEC surveys that began in October 2011, flown with a Skymaster. Different breakpoints entirely, running out to 4 nmi.

Odd codes are the left (port) side of the track, even codes the right (starboard). Code 0 means directly on the track-line and applies only to the AT-11, because of the Skymaster's restricted downward visibility.

Open-ended bins

The top bin of every scheme is open (>1, >2, >4 nmi), so distend is Inf. This function reports the code book as the handbook defines it and does not truncate. A detection function cannot be fitted to an unbounded bin, so an analysis that fits one has to choose a truncation distance — and that choice belongs to the analysis rather than to the code book.

References

Kenney, R.D. (2023) The North Atlantic Right Whale Consortium Database: A Guide for Users and Contributors, Version 8, section 8.A.31. NARWC Reference Document 2023-01.

Kenney, R.D. and Scott, G.P. (1981) Calibration of the Beechcraft AT-11 forward observation bubble for population estimation purposes. In CETAP, A Characterization of Marine Mammals and Turtles in the Mid- and North-Atlantic Areas of the U.S. Outer Continental Shelf, Annual Report for 1979. Bureau of Land Management, Washington, DC.

Examples

narwc_strip_bins("nlpsc")
#> # A tibble: 14 × 4
#>     code side  distbegin distend
#>    <dbl> <chr>     <dbl>   <dbl>
#>  1     1 left         0     232.
#>  2     2 right        0     232.
#>  3     3 left       232.    463 
#>  4     4 right      232.    463 
#>  5     5 left       463     926 
#>  6     6 right      463     926 
#>  7     7 left       926    1852 
#>  8     8 right      926    1852 
#>  9     9 left      1852    3704 
#> 10    10 right     1852    3704 
#> 11    11 left      3704    7408 
#> 12    12 right     3704    7408 
#> 13    13 left      7408     Inf 
#> 14    14 right     7408     Inf 
narwc_strip_bins("cetap", platform = "at-11", units = "nmi")
#> # A tibble: 15 × 4
#>     code side     distbegin distend
#>    <dbl> <chr>        <dbl>   <dbl>
#>  1     0 on-track     0       0    
#>  2     1 left         0       0.25 
#>  3     2 right        0       0.25 
#>  4     3 left         0       0.125
#>  5     4 right        0       0.125
#>  6     5 left         0.125   0.25 
#>  7     6 right        0.125   0.25 
#>  8     7 left         0.25    0.5  
#>  9     8 right        0.25    0.5  
#> 10     9 left         0.5     0.75 
#> 11    10 right        0.5     0.75 
#> 12    11 left         0.75    1    
#> 13    12 right        0.75    1    
#> 14    13 left         1     Inf    
#> 15    14 right        1     Inf