共查询到7条相似文献,搜索用时 15 毫秒
1.
Kalikhman I 《Environmental monitoring and assessment》2002,76(3):275-289
A mathematical model was used to examine the effects of a zigzagsurvey design on the adequacy of reconstructing patchy distribution fields. The model simulates fish or plankton patches(or gaps) of different shapes and spatial orientations, and an acoustic survey by a set of transects forming a zigzag. Adequacyof the reconstructed fields to those originally generated was evaluated by calculating their correlations (r). A prioriinformation on the autocorrelation radius for the field in thedirection of a survey (R) allows optimization of survey design and the algorithm of data analysis. A patchy field can be reconstructed properly (r > 0.80) if the distance between transects D < (1.0–1.5)R. If a priori information onthe field is not available, the autocorrelation radius should bedetermined when reconstructing the field, i.e. a posteriori. In cases of field movement, the criterion for choosing a survey direction is based on the relationship betweenthe dimension of moving patches in the direction of movement andthat of the surveyed area. The results obtained indicate that, for a fixed transect spacing, zigzag pattern allow less adequatereconstruction of an original distribution field (in cases of both immovable and movable fields) than corresponding parallel pattern. 相似文献
2.
Patchy Distribution Fields: Sampling Distance Unit of an Interleaved Survey and Reconstruction Adequacy 总被引:1,自引:1,他引:0
Kalikhman I 《Environmental monitoring and assessment》2006,118(1-3):147-163
A mathematical model was used to examine the effects of choosing various units of sampling distance of an interleaved (two-pass)
acoustic survey on the adequacy of reconstructing patchy distribution fields. The model simulates fish or plankton patches
(or gaps) of different shapes and spatial orientations, and an interleaved survey by parallel or zigzag transects, along which
a unit of sampling distance is set. The efficiency of a survey is determined by the adequacy of a reconstructed field to that
originally generated, which is evaluated by calculating their correlations (r). Regarding immovable fields, the experiments conducted indicate that a patchy field can be reconstructed properly (r
2 > 0.70) if the distance between transects D < (1.5–2.0)R and the unit of sampling distance d < (1.5– 2.0)R
p. As, for regular surveys d < (1.0–1.5)R
p, it may be concluded that interleaved surveys are more efficient than regular ones because of the factor studied. In regard
to movable fields, a comparison of the results of interleaved surveys with those of regular surveys directly indicates that
the former may ensure a more adequate field reconstruction than the latter do. This fact confirms the previous conclusion
that an interleaved survey is expedient in cases where there is no preference regarding the position of a vessel for further
work. 相似文献
3.
Kalikhman I 《Environmental monitoring and assessment》2007,124(1-3):243-252
A mathematical model was used to examine the effects of a spiral survey design on the adequacy of reconstructing patchy distribution
fields. The model simulates fish or plankton patches (or gaps) of different shapes and spatial orientations, and acoustic
surveys by a spiral of Archimedes; for comparison, surveys by parallel or zigzag transects are imitated. Adequacy of the reconstructed
fields to those originally generated was evaluated by calculating their correlations (r). The mathematical experiments conducted
showed that spiral surveys ensure, practically speaking, the same adequacy of field reconstruction (both in cases of immovable
or movable patches) as do surveys by parallel or zigzag transects with greater sampling effort (overall path). In the case
of a spiral survey, a patchy field can be reconstructed properly (r2 = 0.70) if the overall survey path is not less than S/Rav = 20–30, where Rav is the autocorrelation radius averaged for various directions. Thus, the results obtained allow us to conclude that a spiral
survey design is expedient in cases that the minimal duration of a survey is a decisive factor for its conduction and there
is a priori information that no onshore-offshore gradients of fish density exist in a region under study. 相似文献
4.
Kalikhman I 《Environmental monitoring and assessment》2005,110(1-3):203-215
A mathematical model was used to compare the effects of a regular (one-pass) or interleaved (two-pass) acoustic survey on
the adequacy of reconstructing patchy distribution fields. The model simulates fish or plankton patches of different shapes
and spatial orientations, and a set of parallel or zigzag transects forming a regular or interleaved acoustic survey. The
efficiency of a survey is determined by the adequacy of a reconstructed field to that originally generated, which is evaluated
by calculating their correlations. Regarding the immovable fields, the efficiency of a regular or interleaved acoustic survey
was tested with the following two alternative assumptions: (1) the entire survey was completed; (2) the survey was interrupted
for some reason at the moment when one transect remained non-accomplished. In the former case, the efficiencies of both acoustic
surveys were nearly the same; in the latter case, the efficiency of an interleaved survey was superior to that of a regular
one. With respect to movable fields, the efficiency of the completed interleaved surveys was even higher than that of the
regular ones. Thus, the results obtained allow us to conclude that an interleaved survey is expedient in cases where there
is no preference regarding the position of a vessel for further work. 相似文献
5.
Kalikhman I 《Environmental monitoring and assessment》2007,129(1-3):197-206
A mathematical model is used to examine the effects of choosing various units of sampling distance of a spiral acoustic survey
on the adequacy of reconstructing patchy distribution fields. The model simulates fish or plankton patches (or gaps) of different
shapes and spatial orientations, and an acoustic survey by a spiral of Archimedes along which a unit of sampling distance
is set. For comparison, surveys are imitated by parallel transects along which the same unit of sampling distance is set.
Adequacy of the reconstructed fields to those originally generated is evaluated by calculating their correlations (r). In the case of a spiral survey, the mathematical experiments conducted show that an immovable field can be reconstructed
properly (r
2 > 0.70) if the ratio of the units of sampling distance to the autocorrelation radius for the field averaged in various directions
d/R
av < 1.0–1.5. Regarding immovable fields, the spiral surveys ensure, practically speaking, the same adequacy of the field reconstruction
as do surveys by parallel transects with the same unit of sampling distance. In regard to movable fields, a comparison of
the results of spiral surveys with those of surveys by parallel transects indicates that the former may ensure even higher
adequacy of the field reconstruction than do the latter, provided that the units of sampling distances in these surveys are
equal to each other. 相似文献
6.
7.
Magnussen S 《Environmental monitoring and assessment》2002,78(1):63-87
Joint maximum likelihood estimates (JML) of category frequencies and change from repeat stratified two-phase samplingsurveys with a fallible classifier are often seriously biased andhave large root mean square errors when they are obtained for small populations (<5000) with three or more categories and amoderate to small phase II sample size (<1000). JML estimates of state also depend on antecedent or posterior data, a recipe for inconsistency. In these situations, a separate maximum likelihood estimation (SML) of category frequenciesat each survey date appears preferable. SML estimates of net change are obtained as the difference in states. SML standard errors of change are obtained via an estimate of the temporal correlation and variances of state. A bivariate binarylogistic model of change provided the estimate of temporal correlation. SML generally outperformed JMLsignificantly in terms of bias and root mean square errors in eight case studies. 相似文献