plus sampling and calculation of line length and coverage scores

[Janet]

Hello, I'm fairly new to survey design with distance sampling so forgive me if this is an obvious answer. I'm designing an equal spaced zigzag survey and we want to use plus sampling to improve coverage at the edges of the region. However, the dsims package in R appears to be calculating line, trackline and cyclic trackline length as well as coverage by including the transect length that falls outside of the region. Is there a way to still apply plus sampling to the design while only calculating effort and coverage within the study region?

Thanks 

Janet

[Eric Rexstad]

Janet

Welcome to the world of survey design.

When using "plus" sampling, survey effort does indeed fall outside the study area, with observers recording detections made inside the study area. As a result, the line length (effort) computed will include portions of transects outside the study area boundary.

Trackline length (that includes between transect travel) will also be outside the study area boundary if the end points of the transects fall outside the study area. Finally, cyclical trackline length (incorporating travel from the end of the final transect to the beginning of the first transect) will also include travel outside the study area if those end points are outside the study area boundary, as they will be in the case of plus sampling.

I would not expect coverage to be miscalculated when using plus sampling. Coverage (in this context) is measured using a grid of points inside the study area boundary defined by the study area shape file. If you think this is not accurate, please provide us with additional details.

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From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of Janet <jlmo...@dal.ca>
Sent: 20 October 2022 18:37
To: distance-sampling <distance...@googlegroups.com>
Subject: [distance-sampling] plus sampling and calculation of line length and coverage scores

 

Hello, I'm fairly new to survey design with distance sampling so forgive me if this is an obvious answer. I'm designing an equal spaced zigzag survey and we want to use plus sampling to improve coverage at the edges of the region. However, the dsims package in R appears to be calculating line, trackline and cyclic trackline length as well as coverage by including the transect length that falls outside of the region. Is there a way to still apply plus sampling to the design while only calculating effort and coverage within the study region?

Thanks 

Janet

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[Janet]

I see - It makes sense that coverage is only calculated within the region. Thanks for the response!