title: Enhancing spatial resolution of remotely sensed data for mapping freshwater environments

authors: Ashraf, Muhammad Salman

subjects: freshwater mapping

abstract: Freshwater environments are important for ecosystem services and biodiversity. These environments are subject to many natural and anthropogenic changes, which influence their quality; therefore, regular monitoring is required for their effective management. High biotic heterogeneity, elongated land/water interaction zones, and logistic difficulties with access make field based monitoring on a large scale expensive, inconsistent and often impractical. Remote sensing (RS) is an established mapping tool that overcomes these barriers. However, complex and heterogeneous vegetation and spectral variability due to water make freshwater environments challenging to map using remote sensing technology. Satellite images available for New Zealand were reviewed, in terms of cost, and spectral and spatial resolution. Particularly promising image data sets for freshwater mapping include the QuickBird and SPOT-5. However, for mapping freshwater environments a combination of images is required to obtain high spatial, spectral, radiometric, and temporal resolution. Data fusion (DF) is a framework of data processing tools and algorithms that combines images to improve spectral and spatial qualities. A range of DF techniques were reviewed and tested for performance using panchromatic and multispectral QB images of a semi-aquatic environment, on the southern shores of Lake Taupo, New Zealand. In order to discuss the mechanics of different DF techniques a classification consisting of three groups was used - (i) spatially-centric (ii) spectrally-centric and (iii) hybrid. Subtract resolution merge (SRM) is a hybrid technique and this research demonstrated that for a semi aquatic QuickBird image it out performed Brovey transformation (BT), principal component substitution (PCS), local mean and variance matching (LMVM), and optimised high pass filter addition (OHPFA). However some limitations were identified with SRM, which included the requirement for predetermined band weights, and the over-representation of the spatial edges in the NIR bands due to their high spectral variance. This research developed three modifications to the SRM technique that addressed these limitations. These were tested on QuickBird (QB), SPOT-5, and Vexcel aerial digital images, as well as a scanned coloured aerial photograph. A visual qualitative assessment and a range of spectral and spatial quantitative metrics were used to evaluate these modifications. These included spectral correlation and root mean squared error (RMSE), Sobel filter based spatial edges RMSE, and unsupervised classification. The first modification addressed the issue of predetermined spectral weights and explored two alternative regression methods (Least Absolute Deviation, and Ordinary Least Squares) to derive image-specific band weights for use in SRM. Both methods were found equally effective; however, OLS was preferred as it was more efficient in processing band weights compared to LAD. The second modification used a pixel block averaging function on high resolution panchromatic images to derive spatial edges for data fusion. This eliminated the need for spectral band weights, minimised spectral infidelity, and enabled the fusion of multi-platform data. The third modification addressed the issue of over-represented spatial edges by introducing a sophisticated contrast and luminance index to develop a new normalising function. This improved the spatial representation of the NIR band, which is particularly important for mapping vegetation. A combination of the second and third modification of SRM was effective in simultaneously minimising the overall spectral infidelity and undesired spatial errors for the NIR band of the fused image. This new method has been labelled Contrast and Luminance Normalised (CLN) data fusion, and has been demonstrated to make a significant contribution in fusing multi-platform, multi-sensor, multi-resolution, and multi-temporal data. This contributes to improvements in the classification and monitoring of fresh water environments using remote sensing.

text: Enhancing spatial resolution of remotely sensed data for mapping freshwater environments Freshwater environments are important for ecosystem services and biodiversity. These environments are subject to many natural and anthropogenic changes, which influence their quality; therefore, regular monitoring is required for their effective management. High biotic heterogeneity, elongated land/water interaction zones, and logistic difficulties with access make field based monitoring on a large scale expensive, inconsistent and often impractical. Remote sensing (RS) is an established mapping tool that overcomes these barriers. However, complex and heterogeneous vegetation and spectral variability due to water make freshwater environments challenging to map using remote sensing technology. Satellite images available for New Zealand were reviewed, in terms of cost, and spectral and spatial resolution. Particularly promising image data sets for freshwater mapping include the QuickBird and SPOT-5. However, for mapping freshwater environments a combination of images is required to obtain high spatial, spectral, radiometric, and temporal resolution. Data fusion (DF) is a framework of data processing tools and algorithms that combines images to improve spectral and spatial qualities. A range of DF techniques were reviewed and tested for performance using panchromatic and multispectral QB images of a semi-aquatic environment, on the southern shores of Lake Taupo, New Zealand. In order to discuss the mechanics of different DF techniques a classification consisting of three groups was used - (i) spatially-centric (ii) spectrally-centric and (iii) hybrid. Subtract resolution merge (SRM) is a hybrid technique and this research demonstrated that for a semi aquatic QuickBird image it out performed Brovey transformation (BT), principal component substitution (PCS), local mean and variance matching (LMVM), and optimised high pass filter addition (OHPFA). However some limitations were identified with SRM, which included the requirement for predetermined band weights, and the over-representation of the spatial edges in the NIR bands due to their high spectral variance. This research developed three modifications to the SRM technique that addressed these limitations. These were tested on QuickBird (QB), SPOT-5, and Vexcel aerial digital images, as well as a scanned coloured aerial photograph. A visual qualitative assessment and a range of spectral and spatial quantitative metrics were used to evaluate these modifications. These included spectral correlation and root mean squared error (RMSE), Sobel filter based spatial edges RMSE, and unsupervised classification. The first modification addressed the issue of predetermined spectral weights and explored two alternative regression methods (Least Absolute Deviation, and Ordinary Least Squares) to derive image-specific band weights for use in SRM. Both methods were found equally effective; however, OLS was preferred as it was more efficient in processing band weights compared to LAD. The second modification used a pixel block averaging function on high resolution panchromatic images to derive spatial edges for data fusion. This eliminated the need for spectral band weights, minimised spectral infidelity, and enabled the fusion of multi-platform data. The third modification addressed the issue of over-represented spatial edges by introducing a sophisticated contrast and luminance index to develop a new normalising function. This improved the spatial representation of the NIR band, which is particularly important for mapping vegetation. A combination of the second and third modification of SRM was effective in simultaneously minimising the overall spectral infidelity and undesired spatial errors for the NIR band of the fused image. This new method has been labelled Contrast and Luminance Normalised (CLN) data fusion, and has been demonstrated to make a significant contribution in fusing multi-platform, multi-sensor, multi-resolution, and multi-temporal data. This contributes to improvements in the classification and monitoring of fresh water environments using remote sensing.

year: 2011

title: Determinants of herbicide use in rice production in the Philippines

authors: Beltran, Jesusa C.

subjects: herbicide use

abstract: This study identifies farm-specific and market factors affecting the adoption of herbicides and the level of herbicide use by rice farmers in the Philippines. This requires the application of a modified version of Heckman's two-step method to estimate a random-effects double-hurdle model for unbalanced panel data. The age of the farmer, household size, and irrigation use are significant determinants of the decision of farmers to adopt herbicides as an alternative to manual weeding, while economic variables such as the price of herbicides, total income, and access to credit determine the level of herbicide use. Determinants of both adoption and level are land ownership, farm area, and the method of crop establishment. These results are potentially relevant when designing policies to reduce excessive herbicide use or to encourage the adoption of alternative weed control methods such as integrated weed management.

text: Determinants of herbicide use in rice production in the Philippines This study identifies farm-specific and market factors affecting the adoption of herbicides and the level of herbicide use by rice farmers in the Philippines. This requires the application of a modified version of Heckman's two-step method to estimate a random-effects double-hurdle model for unbalanced panel data. The age of the farmer, household size, and irrigation use are significant determinants of the decision of farmers to adopt herbicides as an alternative to manual weeding, while economic variables such as the price of herbicides, total income, and access to credit determine the level of herbicide use. Determinants of both adoption and level are land ownership, farm area, and the method of crop establishment. These results are potentially relevant when designing policies to reduce excessive herbicide use or to encourage the adoption of alternative weed control methods such as integrated weed management.

year: 2013

title: Indigenous challenges to enhance freshwater governance and management in Aotearoa New Zealand - the Waikato river settlement

authors: Te Aho, Linda

subjects: New Zealand

abstract: Co-management of environmental resources is an idea that has been developing for some time in Aotearoa New Zealand as a strategy that recognises Indigenous interests in the environment, and the different ways that people view the world. The contest for control of New Zealand's rivers has generally arisen from successive governments purporting to secure rights based upon English common law. Precepts of that law were completely foreign to the Indigenous Maori who had their own conceptions of rivers. Through the eyes of the Maori, rivers have their own life force, their own spiritual energy and their own powerful identities. Rivers are inextricably linked to tribal identities. Over time a raft of policies was employed and legislation passed by parliament in the name of development and the national interest which did not take into account Maori understandings of the river and its ecosystems, nor their rights, interests, or authority. Excluded from decision-making processes, Maori have long brought matters to the attention of courts by using any basis to assert our rights and interests, and to have our concerns about the deteriorating health and wellbeing of our rivers taken seriously. The search for redress has been relentless. The Resource Management Act 1991 formalised a range of legal rights, but such rights can be meaningless if presented as just one of many other considerations that decision-makers have to take into account. This article explores the notion of collaborative management and the development of co-management models as a background to the emergent Waikato River settlement ± a legal solution embedded in the Waikato-Tainui Raupatu Claims (Waikato River) Settlement Act 2010 that generates a more robust opportunity to bring to an end a paradigm of exclusion and usher in a new era that promises enhanced governance and management of a significant waterway.

text: Indigenous challenges to enhance freshwater governance and management in Aotearoa New Zealand - the Waikato river settlement Co-management of environmental resources is an idea that has been developing for some time in Aotearoa New Zealand as a strategy that recognises Indigenous interests in the environment, and the different ways that people view the world. The contest for control of New Zealand's rivers has generally arisen from successive governments purporting to secure rights based upon English common law. Precepts of that law were completely foreign to the Indigenous Maori who had their own conceptions of rivers. Through the eyes of the Maori, rivers have their own life force, their own spiritual energy and their own powerful identities. Rivers are inextricably linked to tribal identities. Over time a raft of policies was employed and legislation passed by parliament in the name of development and the national interest which did not take into account Maori understandings of the river and its ecosystems, nor their rights, interests, or authority. Excluded from decision-making processes, Maori have long brought matters to the attention of courts by using any basis to assert our rights and interests, and to have our concerns about the deteriorating health and wellbeing of our rivers taken seriously. The search for redress has been relentless. The Resource Management Act 1991 formalised a range of legal rights, but such rights can be meaningless if presented as just one of many other considerations that decision-makers have to take into account. This article explores the notion of collaborative management and the development of co-management models as a background to the emergent Waikato River settlement ± a legal solution embedded in the Waikato-Tainui Raupatu Claims (Waikato River) Settlement Act 2010 that generates a more robust opportunity to bring to an end a paradigm of exclusion and usher in a new era that promises enhanced governance and management of a significant waterway.

year: 2010