title: Using acoustic backscatter data to provide estimates of profiles of suspended sediment concentrations for cohesive particles in the field

authors: Redder, Isabella Julie

subjects: Acoustic backscatter

abstract: Many estuaries and rivers in New Zealand and other locations worldwide are stressed by the input of fine (muddy) sediments. Suspended sediment concentrations (SSC) are often used as a key indicator of water quality and are a critical variable in management practices to aid in the health of estuarine habitats. However, robust measurements of SSC are difficult to obtain, owing in part to large gradients in conditions, and the process of ‘flocculation’ or aggregation of fine particles. Amongst the range of measurement tools available, acoustic backscatter (ABS) sensors offer significant potential to provide temporally and spatially well resolved profiles of SSC from the field. The process of ‘inversion’ or converting the acoustic backscatter signal into SSC is effective when all terms are known within the theoretical context. However, the challenge facing the use of ABS technology in the field, is the scattering properties, the form function f∞ and the total scattering cross-section Σₛ, of cohesive particles typical in estuarine environments, are unknown.

For this study, a unique laboratory calibration combined with ABS field data from a mudflat, were used to investigate if a pair of f∞ and Σₛ values could be evaluated for finer grain, mud material as opposed to sand particles. The derived f∞ and Σₛ values appeared to be influenced by other physical controls from the field environment and were sensitive to several assumptions made in the inversion equation. Nonetheless, the acoustic data yielded reasonable estimates of SSC in a field setting, when compared to discrete single-point measurements of SSC obtained from a calibrated optical backscatter sensor. However, there were also times when the inversion methodology did not work well (particularly for acoustic transducers with lower frequencies). Moreover, inversion results were better when using time-varying values for f∞ and Σₛ, the inversion procedure implemented with a universal set parameters did not perform as well. These results imply more research is needed in gathering better descriptions of the f∞ and Σₛ values from multiple ABS frequencies, to improve inversion SSC results from the field.

text: Using acoustic backscatter data to provide estimates of profiles of suspended sediment concentrations for cohesive particles in the field Many estuaries and rivers in New Zealand and other locations worldwide are stressed by the input of fine (muddy) sediments. Suspended sediment concentrations (SSC) are often used as a key indicator of water quality and are a critical variable in management practices to aid in the health of estuarine habitats. However, robust measurements of SSC are difficult to obtain, owing in part to large gradients in conditions, and the process of ‘flocculation’ or aggregation of fine particles. Amongst the range of measurement tools available, acoustic backscatter (ABS) sensors offer significant potential to provide temporally and spatially well resolved profiles of SSC from the field. The process of ‘inversion’ or converting the acoustic backscatter signal into SSC is effective when all terms are known within the theoretical context. However, the challenge facing the use of ABS technology in the field, is the scattering properties, the form function f∞ and the total scattering cross-section Σₛ, of cohesive particles typical in estuarine environments, are unknown.

For this study, a unique laboratory calibration combined with ABS field data from a mudflat, were used to investigate if a pair of f∞ and Σₛ values could be evaluated for finer grain, mud material as opposed to sand particles. The derived f∞ and Σₛ values appeared to be influenced by other physical controls from the field environment and were sensitive to several assumptions made in the inversion equation. Nonetheless, the acoustic data yielded reasonable estimates of SSC in a field setting, when compared to discrete single-point measurements of SSC obtained from a calibrated optical backscatter sensor. However, there were also times when the inversion methodology did not work well (particularly for acoustic transducers with lower frequencies). Moreover, inversion results were better when using time-varying values for f∞ and Σₛ, the inversion procedure implemented with a universal set parameters did not perform as well. These results imply more research is needed in gathering better descriptions of the f∞ and Σₛ values from multiple ABS frequencies, to improve inversion SSC results from the field.

year: 2023

title: On the chromatic index of Latin squares

authors: Cavenagh, Nicholas J.

abstract: A proper coloring of a Latin square of order n is an assignment of colors to its elements triples such that each row, column and symbol is assigned n distinct colors. Equivalently, a proper coloring of a Latin square is a partition into partial transversals. The chromatic index of a Latin square is the least number of colors needed for a proper coloring. We study the chromatic index of the cyclic Latin square which arises from the addition table for the integers modulo n. We obtain the best possible bounds except for the case when n=2 is odd and divisible by 3. We make some conjectures about the chromatic index, suggesting a generalization of Ryser's conjecture (that every Latin square of odd order contains a transversal).

text: On the chromatic index of Latin squares A proper coloring of a Latin square of order n is an assignment of colors to its elements triples such that each row, column and symbol is assigned n distinct colors. Equivalently, a proper coloring of a Latin square is a partition into partial transversals. The chromatic index of a Latin square is the least number of colors needed for a proper coloring. We study the chromatic index of the cyclic Latin square which arises from the addition table for the integers modulo n. We obtain the best possible bounds except for the case when n=2 is odd and divisible by 3. We make some conjectures about the chromatic index, suggesting a generalization of Ryser's conjecture (that every Latin square of odd order contains a transversal).

year: 2015

title: Mōteatea: He pātaka whakairinga kōrero nō Ngāti Rangiwewehi

authors: Paterson, Awatea

subjects: Ngāti Rangiwewehi

abstract: Mai rā anō a Ngāi Tāua, te iwi Māori, e tuku iho ai i ngā mātauranga mā te ārero tupuna mai i tētehi whakatupuranga, ki tētehi whakatupuranga. Ko ngā mātauranga ka tukua iho ko ngā pūrākau, ko ngā karakia, ko ngā whakataukī, ā, ko ngā waiata hoki. Ko te pūtake o te rangahau nei he titiro pū ki te āhua o te noho o ngā mōteatea hei pātaka whakairinga kōrero mō Ngāti Rangiwewehi ake, nō reira ka āta tirohia ngā momo puna mōhiohio, ngā momo kura aweko ka whakairia ki te pakitara o te pātaka kōrero o Ngāti Rangiwewehi. Nā ngā mōteatea i tohu te wā, i kōrero mō te wāhi, i whakapūkete ngā mahi a ngā tūpuna o te wā i titoa ai te mōteatea. Nā, ko ngā waiata, ko ngā mōteatea koirā te ara whakapūkete kōrero ka wānangahia e te tuhinga nei. Mā te āta wetewete i tētehi mōteatea pū o Ngāti Rangiwewehi, ka hora i ngā kura āuki, i ngā māpihi pounamu, i ngā puna mātauranga o te iwi kua whakaemi mai ki roto i te mōteatea hei kōrero tuku iho mō te iwi o Ngāti Rangiwewehi, hei whakatauira ake hoki i te āhua o te noho o ngā mōteatea hei ara whakapūkete mātauranga.

text: Mōteatea: He pātaka whakairinga kōrero nō Ngāti Rangiwewehi Mai rā anō a Ngāi Tāua, te iwi Māori, e tuku iho ai i ngā mātauranga mā te ārero tupuna mai i tētehi whakatupuranga, ki tētehi whakatupuranga. Ko ngā mātauranga ka tukua iho ko ngā pūrākau, ko ngā karakia, ko ngā whakataukī, ā, ko ngā waiata hoki. Ko te pūtake o te rangahau nei he titiro pū ki te āhua o te noho o ngā mōteatea hei pātaka whakairinga kōrero mō Ngāti Rangiwewehi ake, nō reira ka āta tirohia ngā momo puna mōhiohio, ngā momo kura aweko ka whakairia ki te pakitara o te pātaka kōrero o Ngāti Rangiwewehi. Nā ngā mōteatea i tohu te wā, i kōrero mō te wāhi, i whakapūkete ngā mahi a ngā tūpuna o te wā i titoa ai te mōteatea. Nā, ko ngā waiata, ko ngā mōteatea koirā te ara whakapūkete kōrero ka wānangahia e te tuhinga nei. Mā te āta wetewete i tētehi mōteatea pū o Ngāti Rangiwewehi, ka hora i ngā kura āuki, i ngā māpihi pounamu, i ngā puna mātauranga o te iwi kua whakaemi mai ki roto i te mōteatea hei kōrero tuku iho mō te iwi o Ngāti Rangiwewehi, hei whakatauira ake hoki i te āhua o te noho o ngā mōteatea hei ara whakapūkete mātauranga.

year: 2013