Spectral Index

Next week a new video work, commissioned by Avantwhatever, and the culmination of almost two years thinking about earth observation and the epistemics of false colour images will be launched in Melbourne. So, in anticipation, I am publishing here the text voiceover from it, which in the video is delivered by Finnish performance artist Suvi Tuominen:

Alunite Index
Atmospherically Resistant Vegetation Index
Atmospheric Penetration Index
Atmospheric Removal Index
Bare Soil Index
Burn Area Index
Calcite Index

In astronomical photography colour images are constructed by coding and displaying invisible wavelengths of the infrared spectrum as red, green and blue: visualising radiation as colour. Multispectral remote sensing turns this technique back upon the Earth’s surface to analyse its composition. Satellite imaging has taken a photographic logic developed for understanding the cosmos and applied it to the analysis of lived landscapes.

Carbonate Index
Carotenoid Reflectance Index
Cellulose absorption Index
Clay Alteration Index
Deforestation Index
Difference Vegetation Index
Disease Water Stress Index

In geology, colour has long been used to identify minerals. In the traditional geological practice of optical mineralogy, polarised light is shone through a thin-section rock sample, which can then be identified by its colour: its index of refraction. In present day geophysics it is not the refraction of white light, but the reflection of the infrared spectrum, that’s used in the remote identification of minerals.

Dolomite Index
Enhanced Vegetation Index
Ferric Iron Alteration Index
Ferrous Silicates Index
Fire Detection Index
Forestry Coverage Index
Global Environment Modelling Index

A computer mouse scans across the desk beneath it with a monocular eye, navigating among the red, green and blue pixels of the screen by measuring pulses of reflected light bouncing back from the surface beneath. Rapid reflections guide the cursor across simulated landscapes. A bounding box is drawn on the screen. A prospecting target is marked on the map.

Green Atmospherically Resistant Index
Green Chlorophyll Index
Green Soil Adjusted Vegetation Index
Healthy Vegetation Index
Infrared Percentage Vegetation Index
Kaolinite Index

A specific combination of wavelengths enables the identification of an individual mineral or the analysis of a certain variable. This is known as a spectral index. There are a potentially infinite number of spectral indexes. Each one requires a chromatic calculation to be made, a false colour image made from three or more discrete frequencies of light radiation: added, subtracted, multiplied or divided by one another mathematically.

We are living through a dramatic acceleration of spectral resolution. It is no longer sufficient to image the world in colour. To target its minerals accurately requires hyperspectral perception: the ability to image individual frequencies separately.

Laterite Index
Leaf Area Index
Leaf Chlorophyll Index
Leaf Water Vegetation Index
Magnesite Index
Methane Index
Modified Chlorophyll Absorption Ratio Index

The LEDs in each pixel of this image are made of a compound of indium, gallium, and either phosphorous—for the reds—or nitrogen—for the blues and greens. Gallium is produced from bauxite, and Indium from either cassiterite or sphalerite. The connection between colour and minerals, so apparent in the history of pigments, persists in digital photography. In electronic images, colour is metallurgy: the mixing of colours is the mixing of metals. The glowing pixels of this image are illuminated metals: colour wrought from rocks.

Modified Triangular Vegetation Index
Moisture Stress Index
Muscovite Index
Normalised Difference Built-up Index
Normalised Difference Glacier Index
Normalised Difference Lignin Index
Normalised Difference Nitrogen Index

When acid is poured onto an image sensor the spectrum spills out. Every colour it has imaged, seeps across its surface in saturated hues. When you cut into pixels, colours pour out. The spent silver of mass analogue photography and the rare metals from the screens of last century’s televisions are settling on sea beds and leaching from landfills to sediment future lithologies. Meanwhile, overhead, orbital eyes analyse reflected spectra, scouring for new deposits.

Normalised Difference Snow Index
Normalised Difference Vegetation Index
Normalised Difference Water Index
Normalised Multi-band Drought Index
Normalised Pigment Chlorophyll Index
Optimised Soil Adjusted Vegetation Index

Hyperspectral imaging operates by vibrating a quartz crystal with specific, audible frequencies to manipulate its refractive index. This compression and decompression of its molecular structure selectively filters the wavelengths of light passing through it. To analyse the composition of the landscape we must look through a resonated rock.

Photochemical Reflectance Index
Plant Senescence Reflectance Index
Quartz Rich Rocks Index
Red Edge Position Index
Renormalised Difference Vegetation Index
Silica Dioxide Index
Soil Adjusted Vegetation Index

Due to its extreme dryness and high exposure to ultra-violet radiation, the Atacama desert has been used as a terrestrial analogue for a Martian landscape. The low levels of nitrates in the soil make both unsuitable for supporting vegetation. To image these remote landscapes with a spectral index is to assume their future function in the production or transmission of energy, data, or images.

To apply a geological index to a landscape implies a concession to its minerals. The extraction of images from the ground precedes the extraction of minerals from the ground. Imaging the planet with this mineral hungry gaze assumes that it exists only to provide for the production of images.

Structure Intensive Pigment Index
Sulphate Index
Transformed Difference Vegetation Index
Triangular Vegetation Index
Water Band Index

My mouse scrolls over landscapes colourised by spectral calculations: pixels of pegmatite and quantified quartz, that will all be refined to reflect and record, transmit and illuminate images. Landscapes optimised for the production of images, images optimised for the production of minerals. Landscapes reproduced on screens, screens reproduced from landscapes. Even when a digital image doesn’t move — the screen it appears on has a ‘refresh rate’. What is the refresh rate of a landscape?

Worldview Improved Vegetative Index
Worldview New Iron Index
Worldview Soil Index
Worldview Water Index

Cameras of crystalline metal survey landscapes, capturing the reflectance of rocks to feed their own futures. Satellites and screens feed on soil adjusted landscapes, transmitting indexed images of normalised deforestation. Colour has become a technology of quantification: endlessly indexing every inch of the earth to calculate the profit from its pixels. What are the worldviews embedded in these spectral indexes? What worldviews do they exclude?

The meaning of the word index is dependent on context. Here it signifies the measurement of a specific condition, or the presence of a certain mineral. In financial markets an index measures the average change in value, of a single commodity or a range of products. To measure the economic viability of a mineral deposit, its volume is calculated by rendering the subterranean space in blocks: pixelating rocks quantifies their value.

Bloomberg Copper Index
Dow Jones Commodity Industrial Metals Index
Dow Jones UBS Aluminium Subindex
Nasdaq Commodity Silver Index
Precious Metals Basket Index
White Metals Basket Index

Indexes of visibility and indexes of valuation. Indexes of visibility and indexes of valuation. Indexes of visibility and indexes of valuation. Indexes of visibility and indexes of valuation.

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