title: Surface projection for mixed pixel restoration

authors: Larkins, Robert L.

subjects: range imaging

abstract: Amplitude modulated full-field range-imagers are measurement devices that determine the range to an object simultaneously for each pixel in the scene, but due to the nature of this operation, they commonly suffer from the significant problem of mixed pixels. Once mixed pixels are identified a common procedure is to remove them from the scene; this solution is not ideal as the captured point cloud may become damaged. This paper introduces an alternative approach, in which mixed pixels are projected onto the surface that they should belong. This is achieved by breaking the area around an identified mixed pixel into two classes. A parametric surface is then fitted to the class closest to the mixed pixel, with this mixed pixel then being project onto this surface. The restoration procedure was tested using twelve simulated scenes designed to determine its accuracy and robustness. For these simulated scenes, 93% of the mixed pixels were restored to the surface to which they belong. This mixed pixel restoration process is shown to be accurate and robust for both simulated and real world scenes, thus provides a reliable alternative to removing mixed pixels that can be easily adapted to any mixed pixel detection algorithm.

text: Surface projection for mixed pixel restoration Amplitude modulated full-field range-imagers are measurement devices that determine the range to an object simultaneously for each pixel in the scene, but due to the nature of this operation, they commonly suffer from the significant problem of mixed pixels. Once mixed pixels are identified a common procedure is to remove them from the scene; this solution is not ideal as the captured point cloud may become damaged. This paper introduces an alternative approach, in which mixed pixels are projected onto the surface that they should belong. This is achieved by breaking the area around an identified mixed pixel into two classes. A parametric surface is then fitted to the class closest to the mixed pixel, with this mixed pixel then being project onto this surface. The restoration procedure was tested using twelve simulated scenes designed to determine its accuracy and robustness. For these simulated scenes, 93% of the mixed pixels were restored to the surface to which they belong. This mixed pixel restoration process is shown to be accurate and robust for both simulated and real world scenes, thus provides a reliable alternative to removing mixed pixels that can be easily adapted to any mixed pixel detection algorithm.

year: 2009

title: Smelt (Retropinna retropinna) population dynamics and predation by rainbow trout (Salmo gairdneri) in Lake Taupo

authors: Stephens, R.T. Theo

abstract: This study examines smelt (Retropinna retropinna) population biology in Lake Taupo, New Zealand, and describes the development of a model which simulated their population dynamics and interactions with rainbow trout (Salmo gairdneri), their principal predator. The model was used to predict the effects of variation in habitat features on smelt population processes and on their consumption by trout. Implications for fisheries management are discussed.
The smelt population was comprised of three year classes. The juvenile 0+ year class occupied only the pelagic zone and fed exclusively on plankton whilst the adult 1+ year class also occupied the littoral zone and insects present there were included in their diet. A few smelt either failed to spawn at two years old or survived spawning. These grew rapidly, fed on larval bullies (Gobiomophus cotidianus) and spawned in late winter. Juvenile smelt reached 28-34mm FL after one year, 40-55mm FL after two years and 60-110mm FL when nearly 3 years old. Growth occurred all year but was most rapid between May and November.
Spawning commenced in October when adults first became abundant in the littoral zone and continued until April. Females often recovered and spawned a second time, 6 - 8 weeks after the first spawning. Males were sexually active for an extended period. Eggs were scattered over sandy areas along beaches in water less than 3.0m deep and in the lower reaches of tributary streams where water currents were sufficient to prevent formation of algal mats and deposition of silt or detritus. Egg mortalities were correlated with water temperature but not with their density, which reached 5000m⁻² off Waihaha Beach and 40,000⁻² in the Waihora and Whanganui streams. Habitat perturbations caused by extreme weather conditions were thought to cause the most serious egg mortalities. Starvation was probably the principal source of larval mortality as there was little predation on 0+ smelt. Larger (730mm) 1+ smelt were the most important item in the diet of rainbow trout, comprising over 80% by volume of items eaten. Trout tended to select the larger smelt available and the intensity of selection was correlated with measures of smelt abundance. Trout generally gathered in places where 1+ smelt densities were high.
Smelt population dynamics were simulated using length and density dependent models for movements between habitat zones, feeding, growth or starvation, breeding and predatory mortality. The form of simulated length frequency distributions largely determined the rates of these processes and was itself modified by the operation of each process. Modal groups occurred at lengths where food intake was equivalent to metabolic maintenance requirements and this was controlled by the interaction of diet breadth, the size structure and quantity of the food resource and the number of fishes sharing the same food particle size range. Growth of modal groups was controlled both by the duration of the spawning season and by seasonality in food resource quantity and size structure. Pelagic productivity and the ratio of littoral to pelagic habitat area were the most influential habitat features controlling smelt densities while densities of medium sized (30-55mm) smelt and water clarity were the most important factors controlling simulated quantities of smelt eaten by individual trout. Trout predation exerted little influence on simulated smelt population dynamics and consequently, the quantity eaten by individual trout was little affected by trout density. This result and comparison with trout stocking rates used in Canada suggest that a 1 - 2 order of magnitude increase in numbers of trout released annually into the larger Rotorua lakes would not significantly reduce their growth rates.

text: Smelt (Retropinna retropinna) population dynamics and predation by rainbow trout (Salmo gairdneri) in Lake Taupo This study examines smelt (Retropinna retropinna) population biology in Lake Taupo, New Zealand, and describes the development of a model which simulated their population dynamics and interactions with rainbow trout (Salmo gairdneri), their principal predator. The model was used to predict the effects of variation in habitat features on smelt population processes and on their consumption by trout. Implications for fisheries management are discussed.
The smelt population was comprised of three year classes. The juvenile 0+ year class occupied only the pelagic zone and fed exclusively on plankton whilst the adult 1+ year class also occupied the littoral zone and insects present there were included in their diet. A few smelt either failed to spawn at two years old or survived spawning. These grew rapidly, fed on larval bullies (Gobiomophus cotidianus) and spawned in late winter. Juvenile smelt reached 28-34mm FL after one year, 40-55mm FL after two years and 60-110mm FL when nearly 3 years old. Growth occurred all year but was most rapid between May and November.
Spawning commenced in October when adults first became abundant in the littoral zone and continued until April. Females often recovered and spawned a second time, 6 - 8 weeks after the first spawning. Males were sexually active for an extended period. Eggs were scattered over sandy areas along beaches in water less than 3.0m deep and in the lower reaches of tributary streams where water currents were sufficient to prevent formation of algal mats and deposition of silt or detritus. Egg mortalities were correlated with water temperature but not with their density, which reached 5000m⁻² off Waihaha Beach and 40,000⁻² in the Waihora and Whanganui streams. Habitat perturbations caused by extreme weather conditions were thought to cause the most serious egg mortalities. Starvation was probably the principal source of larval mortality as there was little predation on 0+ smelt. Larger (730mm) 1+ smelt were the most important item in the diet of rainbow trout, comprising over 80% by volume of items eaten. Trout tended to select the larger smelt available and the intensity of selection was correlated with measures of smelt abundance. Trout generally gathered in places where 1+ smelt densities were high.
Smelt population dynamics were simulated using length and density dependent models for movements between habitat zones, feeding, growth or starvation, breeding and predatory mortality. The form of simulated length frequency distributions largely determined the rates of these processes and was itself modified by the operation of each process. Modal groups occurred at lengths where food intake was equivalent to metabolic maintenance requirements and this was controlled by the interaction of diet breadth, the size structure and quantity of the food resource and the number of fishes sharing the same food particle size range. Growth of modal groups was controlled both by the duration of the spawning season and by seasonality in food resource quantity and size structure. Pelagic productivity and the ratio of littoral to pelagic habitat area were the most influential habitat features controlling smelt densities while densities of medium sized (30-55mm) smelt and water clarity were the most important factors controlling simulated quantities of smelt eaten by individual trout. Trout predation exerted little influence on simulated smelt population dynamics and consequently, the quantity eaten by individual trout was little affected by trout density. This result and comparison with trout stocking rates used in Canada suggest that a 1 - 2 order of magnitude increase in numbers of trout released annually into the larger Rotorua lakes would not significantly reduce their growth rates.

year: 1984

title: Māori men, relationships, and everyday practices: towards broadening domestic violence research

authors: King, Pita

subjects: Māori

abstract: Relationships are central to the health and wellbeing of Māori (indigenous people of New Zealand). Through processes of colonisation, cultural ways of relatedness embedded within Māori social structures experienced disruption and were reshaped over decades of assimilation. Māori knowledge and everyday practices that assisted in protecting Māori from societal problems, such as domestic violence, began to dwindle. In contemporary New Zealand, Māori are over-represented in domestic violence statistics. Utilising an auto-ethnographic approach and case studies, our research focuses on five Māori men’s experiences within intimate relationships and whānau (extended family) life. A significant feature of this research is that it provides insights into the ways Māori men draw on their cultural ways-of-being to enhance intimate relationships and maintain bonds within whānau and community life to forge new ways-of-being. Such insights have the potential to inform preventative measures against domestic violence within Māori communities.

text: Māori men, relationships, and everyday practices: towards broadening domestic violence research Relationships are central to the health and wellbeing of Māori (indigenous people of New Zealand). Through processes of colonisation, cultural ways of relatedness embedded within Māori social structures experienced disruption and were reshaped over decades of assimilation. Māori knowledge and everyday practices that assisted in protecting Māori from societal problems, such as domestic violence, began to dwindle. In contemporary New Zealand, Māori are over-represented in domestic violence statistics. Utilising an auto-ethnographic approach and case studies, our research focuses on five Māori men’s experiences within intimate relationships and whānau (extended family) life. A significant feature of this research is that it provides insights into the ways Māori men draw on their cultural ways-of-being to enhance intimate relationships and maintain bonds within whānau and community life to forge new ways-of-being. Such insights have the potential to inform preventative measures against domestic violence within Māori communities.

year: 2017