John R. Dymond

Correcting satellite imagery for the variance of reflectance and illumination with topography

Steephill and mountain slopes severely affect remote sensing of vegetation. The irradiation on a slope varies strongly with slope azimuth relative to the sun, and the reflectance of the slope varies with the angles of incidence and exitance relative to the slope normal. Topographic correction involves standardizing imagery for these two effects. We use an atmospheric model with a Digital Elevation Model (DEM) to calculate direct and diffuse illumination, and a simple function of incidence and exitance angles to calculate vegetation-canopy reflectance on terrain slope. The reflectance correction has been derived from the physics of visible direct radiation on a vegetation canopy, but has proved applicable to infrared wavelengths and only requires solar position, slope and aspect. We applied the reflectance and illumination correction to a SPOT 4 image of New Zealand to remove topographic variation. In all spectral bands, the algorithm markedly reduced the coefficients of variation of vegetation groups on rugged terrain. This produced clean spectral signatures, improving the capacity for automated classification. If illumination correction is performed alone, the coefficients of variation can be increased, and so should not be applied without a reflectance correction. The algorithm output is reflectance on a level surface, enabling the monitoring of vegetation in hilly and mountainous areas.

Sediment budget to assess the geomorphic effect of a cyclonic storm, New Zealand

Abstract A short-term sediment budget was constructed to assess the erosion response of a soft-rock hill country watershed to an intense rainstorm event. The watershed is located in a landslide-prone area on the east coast of the North Island, New Zealand. During March 1988, 753 mm of rain was recorded over a four-day period with 320 mm and 329 mm on successive days. Known as Cyclone Bola, this was the largest rainstorm event in the Tutira watershed in the 93-year rainfall record. The budget quantifies the total sediment generated during the storm, the relative contribution of erosion processes involved, the amount of sediment held in storage and the amount discharged into two lakes within the watershed. A landform map of the watershed was constructed and the contribution of each landform type to the total budget was calculated. A total of 1.35 (±0.13) million m3 of sediment was generated during the storm at an average of 420 m3/ha. This is equivalent to a denudation value of 42 mm for the total watershed (3208 ha) and 83 mm for the landforms severely affected by landsliding (1427 ha). Of the sediment generated, 21% remained on hillslopes, 22% was deposited on valley floors, 51% was deposited on the lakebeds and the remaining 6% was discharged from the watershed via the lake outlet. Most of the sediment generated during the storm was from primary source areas on hill slopes, with sediment in secondary storage providing only a small contribution. Landslide erosion was the main process, accounting for 89% of the sediment generated. Channel, tunnel gully and sheet erosion were only minor contributors to the budget. Six hillslope landforms, which occupy only 44% of the watershed generated 90% of the sediment. The results of this sediment budget, when put in context with the storm magnitude-frequency history being analysed from lake cores, contribute to the identification of sustainable land use and management of soft-rock hill country.

Correction of the topographic effect in remote sensing

We derive a formula for the dependence of vegetation-canopy reflectance on terrain slope (visible light only). Reflectance is inversely proportional to the sum of cosine of incidence angle and cosine of exitance angle. Laboratory measurements of miniature forest canopies set up on inclined slopes compare well with predicted reflectances.

Assessment of multiple ecosystem services in New Zealand at the catchment scale

The ecosystem services approach to resource management considers all services provided by ecosystems to all sections of the community. As such, it could be used to assess sustainability of human development and equity in resource use. To facilitate the approach, tools are required at the level of detail at which policy and management decisions are made. We have developed spatially explicit models of indicators of important ecosystem services in New Zealand: regulation of climate, control of soil erosion, regulation of water flow (quantity), provision of clean water (quality), provision of food and fibre, and provision of natural habitat. The models were developed using lookup tables from process-based models to allow rapid evaluation of land-use scenarios. We demonstrate the application of the models to assess ecosystem services in a simulation of hill-country afforestation in the Manawatu catchment, which has recently seen increasing soil erosion in the hills leading to sedimentation of waterways. Each ecosystem service was assessed by calculating the change in the indicator relative to two extremes. The ecosystem services with the largest relative changes were control of soil erosion, carbon sequestration, and provision of wood.

Computer simulation of shallow landsliding in New Zealand hill country

RESUMEN Wu, W. & R.C. Sidle, 1995. A distributed slope stability model for steep forested basins. Water Resources Research 31: 2097- 21 10. A fines del siglo 19, muchas de las Areas colinadas en la lsla Norte de Nueva Zelanda cambiaron de una cobertura de bos- que a pastizales, dejando las vertientes expuestas a desliza- mientos durante lluvias fuertes. Excesivas perdidas de suelo han llevado a cuestionar la sostenibilidad del sistema pastoril, y el increment0 de sedimentaci6n ha causado problemas aguas abajo, tales coma mayores riesgos de inundacidn y la degrada- ci6n de 10s habitats piscicolas. Se necesita un modelo ero- si6n por deslizamientos y de entrega de sedimentos a 10s rios a nivel de cuenca, para ayudar a planificar la conservacibn de suelos y mitigar 10s efectos en las Areas circunvecinas. Se descri- be un modelo de simulaci6n computarizado de deslizamientos superficiales y de la entrega asociada de sedimentos a 10s rios, basado en un modelo digital de terreno (MDT) de alta resolu- ci6n. La probabilidad de producirse deslizamientos durante una tormenta se determina para cada celda del MDT a partir de las capas de informaci6n de un SIG (sistema de informaci6n geo- grdfica), incluyendo sistemas de terreno, Iluvia, vegetaci6n / cobertura de las tierras, y pendiente. Donde ocurren desliza- mientos, estos se mueven a lo largo de las vertientes hacia abajo, dejando una huella de sedimentos de aproximadamente 20 cm de espesor en promedio, hasta que alcanzan un rio o hasta que el movimiento se debilita. La tasa de producci6n de sedimentos puede calcularse para cualquier area. Se demuestra la bondad del modelo, evaluando 10s efectos de dos escenarios de reforestacidn en la pPrdida de suelos y en la produccibn de sedimentos para el case de un fuerte aguacero simulado en la cuenca de Waipaoa (220 x 103 ha), mediante el uso de un MDT de 3200 x 3600 celdas de 25 cm.

Directional reflectance of vegetation measured by a calibrated digital camera

Obtaining directional reflectance information for vegetation canopies is often an expensive and time-consuming process. We present here a simple approach based on the use of an inexpensive digital camera equipped with a wide-angle lens. By the imaging of a large homogeneous area, a single image captures multiple views of a vegetation canopy. This gives a directional reflectance distribution fully sampled for view direction and free of variations in Sun elevation and azimuth. We determined the radiometric response of the camera sensor CCDs at the focal point and then extended this calibration to the full CCD array by using averaged images of clear blue sky. We evaluated the utility of the system by obtaining directional reflectance distributions of two vegetation targets, grass (Lolium spp) and pine forest (Pinus radiata), for red visible light. The precision of the derived biangular pattern of reflectance was +/-7%.

Integrated catchment management—interweaving social process and science knowledge

This paper provides an overview of the Motueka integrated catchment management (ICM) research programme. This research was based on the thesis that achieving ecosystem resilience at a catchment scale requires active measures to develop community resilience. We define a generic adaptive planning and action process, with associated knowledge management and stakeholder involvement processes, and illustrate those processes with observations from five research themes: (1) water allocation; (2) land use effects on water; (3) land and freshwater impacts on the coast; (4) integrative tools and processes for managing cumulative effects; and (5) building human capital and facilitating community action. Our research clearly illustrates the benefits for effective decision-making of carrying out catchment scale science and management within collaborative processes which patiently develop trusting relationships. We conclude that coastal catchments should be managed as a holistic continuum from ridge tops to the sea and that some processes like floods or loss of community resilience have decadal consequences, which support the need for long-term monitoring and investment.

BRDF Correction of Vegetation in AVHRR Imagery

In this article we present a method for correcting AVHRR visible and near-infrared imagery for varying satellite and solar zenith angles. This method is based on the WAK BRDF model for closed canopies. The parameters required to perform BRDF correction can be derived from consecutive pass AVHRR imagery pairs. This imagery provides two views of the land surface close together in time but with large differences in phase angle. It is reasonable to assume that both the surface and the atmosphere will change little between orbits, and that after BRDF correction reflectances of given targets should be the same in both orbits. Before BRDF parameters can be fitted, atmospheric correction must be performed. To improve this process, average monthly atmospheric profiles and aerosol optical depths are used as radiative transfer model inputs in conjunction with a digital elevation model. Using atmosphere corrected reflectance data from 12 NOAA-14 AVHRR image pairs, BRDF parameters were extracted for predominant vegetation groups in New Zealand: indigenous forest; exotic forest; scrub; pasture; and tussock grassland. For each of these vegetation groups significant non-Lambertian reflectance behavior was observed, and BRDF correction using the derived parameters successfully minimized this variation. Measuring the spread of the corrected results from the desired equal reflectance line gives a measure of the accuracy of the method. After correction, the RMS reflectance errors were approximately 0.01 in the visible and 0.02 in the near-infrared. A vegetation map specifying the proportions of the vegetation groups at any given location can be used to perform regular BRDF correction. Reflectance standardization to a fixed view and sun angle can then be performed using the pre-derived BRDF parameters and proportional BRDF correction.

A Python-Based Open Source System for Geographic Object-Based Image Analysis (GEOBIA) Utilizing Raster Attribute Tables

A modular system for performing Geographic Object-Based Image Analysis (GEOBIA), using entirely open source (General Public License compatible) software, is presented based around representing objects as raster clumps and storing attributes as a raster attribute table (RAT). The system utilizes a number of libraries, developed by the authors: The Remote Sensing and GIS Library (RSGISLib), the Raster I/O Simplification (RIOS) Python Library, the KEA image format and TuiView image viewer. All libraries are accessed through Python, providing a common interface on which to build processing chains. Three examples are presented, to demonstrate the capabilities of the system: (1) classification of mangrove extent and change in French Guiana; (2) a generic scheme for the classification of the UN-FAO land cover classification system (LCCS) and their subsequent translation to habitat categories; and (3) a national-scale segmentation for Australia. The system presented provides similar functionality to existing GEOBIA packages, but is more flexible, due to its modular environment, capable of handling complex classification processes and applying them to larger datasets.

Nitrate and phosphorus leaching in New Zealand: a national perspective

Abstract Excessive amounts of nutrients in rivers promote biological growth of periphyton and macrophytes to nuisance levels. Of most concern, because they are immediately available for growth, are dissolved inorganic forms of nitrogen (N) and phosphorus (P), primarily as nitrate-N and dissolved reactive phosphorus (DRP). To help understand the sources of dissolved nutrients, we estimated and mapped subsurface flow (i.e. leaching) losses of nitrate and DRP. There are large areas of high nitrate leaching in Waikato, Bay of Plenty, Taranaki and Canterbury. The high spatial detail of the maps permits use for planning mitigation at local, regional and national scales. However, they should not be used to infer leaching rates for particular farms as average farming practices are assumed. The nitrate leaching maps were driven primarily by animal numbers, so regional trends of total leached nitrate between 1990 and 2010 were able to be determined from regional statistics of farm animals.