New Zealand From Space

Forest and Bird, Issue 311, 1 February 2004, Page 19

New Zealand From Space

GORDON ELL

New satellite technology reveals what development is doing

to the earth.

spoke with ALISTAIR PEARCE of

Terralink international.

he sight of New Zealand from up to | 900 kilometres out in space reveals a changing land. Surprisingly, from that distance it is still possible to resolve detail down to a mere 20 metres. A new book, produced by the mapping agency Terralink International, presents a variety of images which highlight the value of taking such a long view. Satellite imagery is providing a prompt, if expensive way of plotting rapid changes in our countryside and the impact of development. Unlike aerial photography, which is the basis of our land maps, satellite pictures

build on digital values garnered from space. By manipulating the digital information, it is possible to highlight specific features to show the nature of change. New Zealand from Space 2 follows an earlier book which simply showed the country from outer space; the new book looks at the patterns and impact of settlement. Lakes, for example, may appear in different colours indicating their relative health. Coastlines accommodating rapid urban sprawl, or development of forested lands for housing, can be promptly identified. Even the increased run-off from development

becomes quickly identifiable from satellite images. The advantage of this technology is the frequency with which the ground may be surveyed. Aerial photography run by conventional aircraft is a time-consuming business; it is traditionally done in summer and is governed largely by weather and changing local conditions. While aerial photographs have been the basis of mapmaking for more than 60 years it requires clear skies day after day as the camera planes run up and down the country at anywhere between one and nine kilometres

above the earth. The overlapping strips can then be used in a stereoscope so the topography can be traced onto maps. The satellite version, however, is much quicker; the digital pictures are taken daily as the satellite passes over New Zealand. If there’s some cloud, then an image taken later in the week can be married in to fill in the gaps. Then it is a matter of assigning colour values to the features required to be highlighted. Pioneer aerial photographs taken in colour a generation ago could record around seven different types of vegetation. The various greens could be rendered as different reds indicating forest types. The modern satellite information is much more subtle: the 24 different shades of forest can be manipulated to show such detail as the different species of beech growing within a mixed beech forest. There are some interpretative problems, according to Alistair Pearce of Terralink International. There is always some cloud cover over New Zealand and that can appear like snow. Water produces different colours and may appear as clouds or snow too. The problem is generally solved by imposing the satellite image over a conventional map which clears up any ambiguities. To produce the images featured in the book, and with this article, digital information from the satellites has been laid over conventional maps. The traditional

contour lines and shading are added in another layer which provides the visual effect of a modelled landscape. Then the maps can be manipulated in any direction to provide a point of view which highlights chosen features. Colouring selected features draws the eye to an interpretation of the landscape, for example the pathway of the trans-alpine highway over Arthur’s Pass and down the Otira Gorge, opposite left. ‘The results can be controversial but we tried to avoid this in our book, says Alistair Pearce of Terralink International, a company formed from the the mapping division of the former Department of Lands and Survey. ‘The results of satellite imagery are much more immediate than the old aerial photography and can show dramatically the changes going on in our environment. He points to an image of the lower Coromandel where developers have been making new waterways for housing development. ‘We could, if we chose, produce satellite images of the impact these changes are having on run-off. ‘Images of the Kapiti coast reflect the rapid spread of housing spilling out from Wellington, he says. ‘Also houses extending into forested areas around Tasman Bay, particularly Kaiteriteri’ The satellite images can be very topical, and very telling. One series by Terralink traces the seasonal spread of the infection Listeria in shellfish. The organism shows up in the water as a red colour. Its daily advance on

mussel farms, for example, can be detected as it spreads along the coast. The four images with this article are typical of the book. Tongariro and Egmont national parks appear in the context of their developed surrounds. In a view from the West Coast, the Arthur’s Pass road makes it way through the Southern Alps and down the Otira Gorge. The images could as easily have been manipulated to give highlighted colour to other features such as land use: indeed another image, which features the abstraction of water from the Rangitata River and its passage across inland MidCanterbury as an irrigation canal to the Rakaia River, shows how available water has intensified farming. Retaken seasonally it would show the irrigated places, the succession of ploughing and cropping, and the extent of pastoralism, according to Alistair Pearce. Terralink is the only former Government agency, reformed into a State-owned enterprise, to go into receivership. Newly re-organised, it is now offering satellitemapping services like this internationally. The book is a showcase of what their map makers can do.

— GORDON ELL

is the editor of Forest & Bird.

Pictures are from New Zealand from Space 2, edited by Rob Phillips, 128pp limpbound, Terralink International/Penguin, Auckland 2003. RRP $39.50.