In 2019 the announcement of the spectrum allocations for 5G mobile communications caused a widely publicised uproar among meteorologists (link). The controversy surrounded the frequency of 23.8GHz, used by weather forecasters for the passive sensing of atmospheric water vapour. Their concern was that 5G radiation between 24.25GHz and 27.5 GHz would interfere with measurements made by weather satellites, affecting the accuracy of forecasting. The impossibility of broadcasting communications at a wavelength of 1.23mm without disrupting sensors tuned to radiation at 1.26mm highlights the increasing competition between science and industry for narrow bandwidths of this frequential space, exemplifying the entanglement of technical media with geophysical phenomena through which the planetary is grasped and produced.
During the 1999 talk in which she coined the term ‘planetarity’, Gayatri Spivak asked us to “think the planet as the proper receiver and transmitter of imperatives”. For Spivak, these ‘imperatives’ are principally the policies and practices of civil society; she speaks for example of “bio-prospecting leading to bio-piracy, leading to monocultures, leading to the death of biodiversity”. But here I would like to focus on understanding Earth as a receiver and transmitter – not so much of imperatives as of signals, frequencies and vibrations – to think the planet spectrally.
In Introduction to Comparative Planetology Lukáš Likavčan proposes the model of a ‘Spectral Earth’, but whereas his understanding is focused on spectres: a planet haunted by the species of its multiple mass extinctions; my understanding of Earth’s spectrality is grounded in the electromagnetic spectrum that surrounds, forms and transforms it, a spectrum that traverses geophysical, technological and geopolitical understandings of the planetary.
The electromagnetic spectrum connects the sensible phenomena of light, sound, heat and vibration in a continuum with the resonant Schumann frequencies of the planet, the toxic wavelengths of ionizing radiation, and the entire history of media communications from radio to 5G. If we centre these spectral phenomena, afford them an equivalent importance in sustaining the biosphere as we commonly do Earth’s unique atmosphere and moist environment, then we can understand the planet as a mass of mineral and organic matter that is immersed in and produced by – that emits, reflects, and absorbs – radiation across the full breadth of the electromagnetic spectrum. The conditions for abundant biodiversity are not only the chemistry of an oxygen-rich atmosphere and water-rich surface but also continuous solar radiation and the cyclical re/production of minerals by tectonic movement and volcanic activity. The infrared spectrum provides warmth from above, while a combination of seismically induced magma flows in the Earth’s core and radioactive isotopes (which, counter-intuitively, are found in greater concentrations in the crust) provide warmth from below. Changes in the absorption and reflection spectra of the planet’s surface directly impact planetary albedo which, as James Lovelock’s Daisyworld model showed, can inflect climate change. According to current climate science “the balance between net incoming solar radiation and outgoing terrestrial radiation at the top of the Earth’s atmosphere fundamentally drives our climate system” (link). Many of the phenomena central to geophysics can therefore be understood spectrally, as the interaction of electromagnetic frequencies with mineral bodies, of the physical repercussions of a spectrum of vibrations spanning the tactile and toxic, in short – of matter in media.
Planetary spectrality however is not only conditioned by these cosmic and geophysical phenomena, but is equally produced by technical media’s harnessing of the electromagnetic spectrum. Earth is wrapped in an atmosphere of broadcast frequencies and microwave communications as well as one of oxygen, nitrogen and carbon dioxide. Cables stretched from molten sand transmit words and images encoded as pulses of invisible infrared at three discrete wavelengths of 850, 1300 and 1550nm. And above ground, the air is so densely packed with transmissions that the allocation of this saturated spectral space increasingly poses logistical challenges and potential interference between competing functions of the same bandwidth. But the spectral relationship between geophysics and technics is not always one of friction. As Gilbert Simondon pointed out, radio wavelengths over 80 metres reflect partially off the Heaviside layer of ionised gases between 90 and 150km altitude in the atmosphere, and wavelengths longer than 800 metres “undergo a veritable metallic reflection” enabling radio transmissions to reach beyond the province of their origin and traverse national borders in a way that the shorter wavelengths used in broadcasting television are unable to. Through such examples we can observe what Yuk Hui describes as a “unity between the geographical milieu and the technical milieu” (link). Spectral technics can conjoin constructively with geophysical conditions to ensure an uninterrupted propagation of the worldview they articulate, or their signal can equally be inhibited, for example by the magnetic pull of large ore bodies in the ground. But, through planetary sensing and monitoring, spectral technics also translate geophysical and atmospheric conditions back into the orbit of the technosphere, visualising and quantifying the planetary. If we accept Peter Haff’s convincing thesis that the technosphere now constitutes a provisional global paradigm (link), then surely it is in large part the harnessing of the full electromagnetic spectrum that has enabled technics to become a geologic force.
This complete technical mobilisation of the electromagnetic environment is entirely reliant on a strict partitioning of the spectrum, on the allocation of discrete bands for specific purposes. In the same way that the prefixes infra- and ultra- (infrared, ultraviolet, infrasound, ultrasound) imply the centrality of anthropologically perceptible regions of the spectrum, the division of wavelengths into long-, short-, radio-, or micro- reference only their technical apparatus or function. For Simondon “these distinctions are never founded on the very nature of the phenomenon considered; they do not exist properly speaking according to physical science but only according to technics”. This is not to say that all such spectral semantics are arbitrary, it is surely no coincidence that the two frequencies of light most productive in photosynthesis correspond with two of the colours to which the human retina is sensitive: red and blue. The dominant wavelengths of our shared spectral environment have shaped the evolution of biological sight and vegetal metabolism. But thinking the spectrum from a purely technical stance leads to thinking of multiple channels of interpenetrating communication and radiation as separable and discrete entities, whose effects can be contained.
Discontinuity is essential to understanding the relationality of spectral phenomena, but continuity is essential to totalising the exchanges of energy between reflected shortwave radiation at the top of the atmosphere and outgoing longwave radiation emitted from Earth, or in Haff’s terminology the “incident solar flux” and the absorption by the biosphere. Simondon illustrates this “antinomy of the continuous and the discontinuous” [2020, p.98] with the example of the photo-electric effect, a phenomenon closely related to the technics photo-voltaic cells and digital photography and one that can be seen as a microcosm of the relationship between solar radiation and terrestrial surface. To understand this energy exchange between photon and electron we must conceive of the photon and electron as discrete particles and yet, as Simondon describes, “when a plate of alkaline metal is illuminated by a beam of light … the free electrons [in the metal] behave as beings equivalent to the continuum”. Particles can exist relationally with one another and behave homogenously.
Understanding the planetary as a spectral entity might help enable us to undo what Simondon refers to as the “two complementary representations of the real” which are “perhaps not merely complementary but really one” and to perceive of the planetary system as one in which the apparently distinct spectral signatures of technical and geophysical phenomena are imbricated and entangled in an energetic exchange whose output fundamentally governs climatic conditions.
I want now to move on to the discussion of a specific spectral technicity that exemplifies the sort of geo–technical entanglements discussed above: Remote Sensing. This technique of infrared data visualisation makes direct use of the photo-electric effect to capture terrestrial surfaces, providing the technosphere with a geological analysis of its bedrock. Depending on how this data is employed, hyperspectral remote sensing has the potential to exacerbate, monitor or perhaps even curb anthropogenic climate impacts.
The 1983 edition of the Manual of Remote Sensing begins with a note from its editor proposing that the geological analysis of infrared satellite imagery could be used as a means of planetary resource accounting. With the spectral resolution of contemporary instruments, it is well within the bounds of technical possibility that the perpetual orbits of remote sensing satellites could enable calculations of remaining reserves of key minerals. However, from today’s perspective, in which such far-sighted resource management still seems a distant goal and remote sensing is increasingly touted as a commercial tool of geological prospecting for the new mineral resources required by the digital economy, it also seems a somewhat naïve proposition.
Geological remote sensing operates by photographing the infrared reflectance spectrum of a terrestrial surface and analysing it with respect to the known spectra of certain target minerals. In this instance the photo-electric effect is central both to the function of the apparatus and to the phenomenon observed. In his 1977 article ‘Spectral Signature of Particulate Minerals’ (link), Graham Hunt discusses the phenomenon of charge transfer as one of the “intrinsic spectral features” of minerals. Charge transfer, he writes: “refers to the process whereby absorbed energy causes an electron to migrate between neighbouring ions”, and it is this differential absorption and transfer of radiant energy by minerals that defines the spectral signature by which remote sensing identifies them. Charge transfer, however, is also the process by which incident photons are converted into electrons in digital imaging, so in remote sensing there exists a unity not of milieu, but of the geological phenomenon observed and the technics of observation. The photographic operation performed in camera mirrors the absorption of radiation by the surface beneath: a purified metallic semiconductor quantifies the charge transfers occurring in terrestrial minerals by charge-transferring the photons they reflect back. The photosensitivity of silicon measures the photosensitivity of the predominantly silicate crust from which it was mined and above which it orbits.
The imbrication of remote sensing with planetary resource ecologies is emphasised by the target applications of current developers of hyperspectral cameras, which include: crop and infrastructure inspection, mining, and geological prospecting. All of these explicitly model or inspect terrestrial space to optimise its use for resource extraction, energy generation or commercial agricultural production. The hyperspectral imaging industry positions itself as the superior technology both to assess unchartered resources and to monitor the efficiency of established operations across multiple industries. These applications perpetuate the accelerating trend of outsourcing inspection and visual analysis as machinic processes, in which visualisation is synonymous with processes of quantification and terrestrial accounting: the image operationalised as a spatial display of geo-data for future economisation.
While the use of remote sensing as a method of geological prospecting is relatively recent, aggregating data from four decades of earth observation satellites enables climate scientists to analyse the spectral signature of global warming and calculate Earth’s radiation ‘budget’. Were the necessary political consensus achieved these techniques could potentially be used to enforce a kind of climatic governance.
Satellite images have three different resolutions, a spatial resolution – measured in metres/pixel, a temporal resolution (more commonly known as the revisit rate) – the number of days between each image of the same location, and a spectral resolution – measured in nanometres of bandwidth that are imaged separately. Each of these resolutions plays a role in the use of satellite remote sensing for climate governance. As with the example of water vapour above, many climatic processes exhibit peaks or troughs at specific frequencies, meaning a fine-grained spectral resolution is required to identify and monitor multiple atmospheric processes with a single instrument, whereas “broadband measurements effectively integrate all the energy across the shortwave or longwave [and] may mask signatures associated with particular climate processes” (link). Once again the technics used in climate modelling requires a segregation of the continuous spectral radiation into discrete bandwidths to disaggregate individual phenomena, as can be seen in the graph below comparing the reflectance of snow and ice with the spectral resolution of various satellite missions.
Among the future satellites currently planned by the European Space Agency is the earth observation mission CO2M or CarbonSat (link), which is currently scheduled for a 2025 launch. The development of CarbonSat was explicitly tied to monitoring global emissions targets at the local level. In the paper outlining the technique of remote sensing CO2 emissions at the pixel level of a satellite image (link), the authors frame their proposal as a means to address the Kyoto protocol’s requirement for independent verification of emission reporting. The ability to make reliable estimates of the carbon output of individual coal-fired power plants is the express target of the mission and the rapid increase in construction of coal power plants in India and China is mentioned anecdotally as a likely cause of future emissions growth. Implicit among the complex technical specifications described is the positioning of European scientific method as a moralising emissions monitor over the coal-fired future of the developing world. In this context it’s hard not to see this satellite mission as an act of what Jack Stilgoe refers to as ‘anticipatory governance’ (link), where the rush to meet the power needs of growing populations in Asia is met in Western Europe with a simultaneous scramble to devise a technocratic means to enforce their emissions commitments.
The spectral specifications for CarbonSat are for sensitivity to 3 bands, one in the near infrared (NIR) and two in the shortwave infrared (SWIR). Of these the NIR resolution is highest at 0.1nm, meaning that in the 747-773nm band 260 discrete measurements will be made for each pixel of the array. The main objective of the scientists developing CarbonSat however relies on its spatial resolution, where, according to their calculations, a 2km2 ground resolution will be sufficient to identify the emissions of a single power station. Spectral enforcement of emissions is only possible by a granular fragmentation of continuous solar radiation and terrestrial surface. As Holly Jean Buck writes (albeit in a different context): “engaging in this breaking apart, diagramming and modelling of the systems is how we have learned to think. Sciences both social and biophysical are doing just this. But it is not working. Another line of approach is needed”.
CarbonSat makes clear the potential for such remote sensed satellite observations to be used in implementing a form of spectral climate governance. And, if humanity were to actively engage in the kind of planetary scale geoengineering experiments surveyed by Buck in After Geoengineering, then these same hyperspectral instruments might provide our most immediate means of analysing their climatic effects. But the governance model suggested by the CarbonSat documents relies on satellite surveillance identifying local rogue polluters, which seems about as likely to reduce global emissions as CCTV cameras are to prevent crime. If another model is needed then it should be one that is capable of connecting both spectral phenomena and populations rather than establishing adversarial oversight. Perhaps conceiving of a spectral planetarity could enable us to abandon what Benjamin Bratton refers to as the “tenuous differentiation of geoculture from geotechnology” and instead realise and build upon the mutually constitutive spectral relations between geotechnics and geophysics.