Estimating the impact of light pollution on quantum communication between QEYSSat and Canadian quantum ground station sites

Daniel Oblak; Katanya B. Kuntz; Mathew Yastremski; Nouralhoda Bayat; Paul J. Godin; Sungeun Oh; Thomas Jennewein; Ziheng Chang

REVIEW 3 major objections 5 minor 27 references

Estimating the impact of light pollution on quantum communication between QEYSSat and Canadian quantum ground station sites

T0 review · 3 major / 5 minor · reviewed 2026-08-11 · deepseek-v4-flash

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Pith's one-line read Light pollution at three Canadian sites is low enough for QEYSSat quantum key links.

desk verdict Useful VIIRS-based screening workflow and honest downlink data, but the uplink QBER thresholds are not yet quantitatively supported. read the letter →

arxiv 2412.14944 v1 pith:S6HM53Y2 submitted 2024-12-19 quant-ph physics.opticsphysics.space-ph

Mathew Yastremski , Paul J. Godin , Nouralhoda Bayat , Sungeun Oh , Ziheng Chang , Katanya B. Kuntz , Daniel Oblak , Thomas Jennewein This is my paper · ORCID

classification quant-phphysics.opticsphysics.space-ph

keywords lightpollutionquantumkeydistributionQEYSSatsatellitecommunicationVIIRSnightskyradianceQBERuplinkanddownlink

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper asks whether stray artificial light from nearby cities would drown out the single-photon signals used in satellite quantum key distribution with Canada's QEYSSat mission. Using ground-based photon-counting measurements at three sites (Waterloo, Calgary, and Priddis) and night-light satellite imagery from VIIRS, the authors estimate background photon rates at the quantum wavelengths of 750–850 nm and convert those into expected quantum bit error rates. They conclude the background rates are tolerable: urban sites should support secure uplinks and downlinks once QEYSSat rises above about 40 degrees elevation, and the rural Priddis site could work from 10 degrees. If right, the result matters because it means quantum ground stations can be located near cities where users and fibre networks are, rather than only in dark-sky sites.

What carries the argument

The load-bearing object is an altitude-angle-dependent scaling law that turns a ground radiance measurement into the photon count a satellite receiver would see pointing down at the same ground. Equation 5 expresses the satellite count as $N_{\rm sat}(\theta)=10^{-0.32\csc\theta}\tan^2(\phi)\csc(\theta)\, r_{\rm sat}^2 N_r/(\alpha r_f)^2$, where $\theta$ is the satellite elevation, $\phi$ the receiver half-angle, $N_r$ the rooftop-measured photon rate, and $\alpha r_f$ the collecting fibre's numerical-aperture radius; the $10^{-0.32\csc\theta}$ factor is the atmospheric transmission model taken from the link-loss literature. For the remote method, VIIRS DNB broadband radiance (500–900 nm) is scaled down to the QKD wavelengths using measured spectral fractions (about 0.7% at 780 and 790 nm and 0.5% at 850 nm at Waterloo) and scaled up by estimated illuminated-area fractions, then fed through the same equation to predict satellite-observed background and QBER.

What would settle it

Point a calibrated instrument at the ground footprint from an aircraft or high tower during a QEYSSat pass and compare the measured footprint-averaged radiance with the rooftop-scaled value; if they disagree by more than the stated uncertainties, the uplink predictions shift. The decisive test is direct: run a QKD uplink to QEYSSat from Waterloo or Calgary and check whether the measured QBER crosses the practical 5% threshold as the satellite crosses 40 degrees elevation.

Watch

Extended reading notes

Core claim

The central claim is that light pollution at the three Canadian quantum ground station sites will not prevent successful quantum uplink and downlink experiments with QEYSSat. The paper shows measured downlink background photon rates stay around 300–1000 Hz at 750–850 nm even under full moon and snow, and that uplink background rates reaching the satellite are on the order of a few thousand hertz for the urban sites and only hundreds for the rural site. From these, the predicted QBER of a downlink pass is below 2% for the Waterloo site, and uplink passes become secure once the satellite is above roughly 40 degrees at Waterloo and Calgary, or above 10 degrees at Priddis. A second claim is that VIIRS Day/Night Band radiance, after scaling for spectral bandwidth and illuminated ground fraction, agrees with local measurements and can be used to remotely screen candidate ground station sites.

Load-bearing premise

The whole estimate rests on treating one rooftop fibre measurement of a nearby parking lot at Waterloo, scaled by visually estimated fractions of illuminated ground, as the average brightness of the entire footprint QEYSSat sees, and on assuming the same light spectrum holds at Calgary and Priddis.

Editorial extensions

If this is right

QEYSSat can perform secure quantum uplinks and downlinks from all three Canadian sites despite urban light pollution.
Urban ground stations in Waterloo and Calgary are usable above about 40 degrees elevation; the rural Priddis site can close links from about 10 degrees.
VIIRS night-light satellite data, with spectral and footprint scaling, gives a remote screening tool for choosing future quantum ground station sites.
Downlink background rates near 1000 Hz and uplink rates of a few thousand hertz define an approximate tolerable noise budget for QEYSSat-class links.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

If the same scaling method is applied elsewhere, cities with similar or lower VIIRS radiance than Calgary (about 105 nW/cm²/sr) can be screened remotely before any on-site visit; the main caveat is that the spectral mixture of street lights varies by region.
Because global artificial light is growing several percent per year, an urban site that passes today may fail within a decade; periodic VIIRS re-screening would track the shrinking margin.
The reported agreement between VIIRS and local data suggests that VIIRS radiance could also be used to retroactively estimate background noise for past satellite-QKD experiments, providing a consistency check for other groups.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Here's my take on the QEYSSat light pollution paper. The useful core is real: the authors have measured downlink sky background at three Canadian sites, shown the rates are in the 300–1000 Hz range with full moon spikes, and demonstrated that VIIRS DNB data can be used to screen candidate ground stations without a site visit. That screening workflow is the paper's actual contribution, and it looks like it works.

The downlink story is solid. The QBER curves in Figure 11 are backed by direct photon counting, and the sub-2% result is believable given the Micius comparison. I have no serious quarrel with the claim that these three sites can support downlinks.

The uplink side is where I'd push back. The QBER numbers in Figure 12 and the 'secure above 40 deg' thresholds depend on a chain of assumptions: the spectral scaling measured at Waterloo is applied to Calgary and Priddis without checking whether street lighting spectra differ; the illuminated-area fractions in the VIIRS footprint are visually estimated with ±20% guesses; and no local radiance measurement at UC or RAO is reported to check the VIIRS-derived uplink numbers. The authors do attach a 40% uncertainty, and the directional conclusion probably survives a factor-of-two error, but the specific elevation thresholds are not quantitatively secure yet. I'd want to see a sensitivity analysis or, better, one night of local ground radiance at each site before mission planners rely on '40 deg' and '10 deg'.

Minor points: the QBER figures don't show their link-budget inputs, which makes them hard to audit; data are 'available on reasonable request,' which in practice means not available. The self-citation to Ref [20] is fine—it's a published parameter-free model.

Bottom line: this is a useful applied paper, aimed at the satellite-QKD community and the QEYSSat mission team. It deserves a serious referee and probably major revision to firm up the uplink predictions. I'd bring it to a reading group if anyone at the table works on ground-station siting.

Referee Report

3 major / 5 minor

Summary. The paper characterizes night-sky and ground-reflected light pollution at three Canadian quantum ground station sites (Waterloo, Calgary, and Priddis) in the 750-850 nm band relevant to the QEYSSat mission. For the downlink, the authors report direct single-photon-counting measurements under new-moon and full-moon conditions at all three sites. For the uplink, they use two estimation routes: a rooftop fibre-radiance measurement at Waterloo and VIIRS Day/Night Band satellite radiance data, scaled by spectral factors measured at Waterloo and by visually estimated illuminated-area fractions, for all three sites. These background rates are fed into a link model to produce predicted QBER curves as a function of satellite elevation. The central claims are that all three sites can support both uplinks and downlinks with QEYSSat, that the urban Waterloo and Calgary sites require elevations above about 40 degrees for uplink, that rural Priddis may work from about 10 degrees, and that VIIRS data can be used to assess candidate sites remotely.

Significance. If its quantitative conclusions hold, the paper would provide a practical, immediately useful input to QEYSSat mission planning and to future ground-station site selection in light-polluted areas. The downlink measurements are a genuine comparative dataset across urban and rural sites under two lunar conditions, and the VIIRS-vs-rooftop comparison at Waterloo is a promising first validation of a remote assessment method. The paper also credits a previously published parameter-free link-loss and atmospheric transmission model rather than fitting new parameters to the target result, which strengthens the internal logic of the analysis. The main limitation is that the quantitative uplink predictions for Calgary and Priddis rest on assumptions that are not yet validated at those sites, so the central mission-planning claim is only partially supported by the evidence presented.

major comments (3)

[Section 2.2, Eqs. (6)-(7), Figs. 8-10] The uplink background estimates for QGS-UC and QGS-RAO are derived from VIIRS DNB radiance scaled by spectral factors measured only at QGS-UW and by visually estimated illuminated-area fractions (approximately 1/3, 3/4, and 1/10 for VIIRS pixels and 3/4, 1/2, and 1/10 for QEYSSat footprints) that are assumed to hold at all three sites. No independent ground-radiance measurement is reported for QGS-UC or QGS-RAO against which the VIIRS-derived uplink rates can be checked, so a factor-of-2 error in the actual footprint radiance would shift the QBER thresholds in Fig. 12 by roughly 10-20 degrees in elevation. The quantitative mission-planning claim therefore rests on an unvalidated transfer of a single-site spectral characterization to the other two sites.
[Section 3.2, Fig. 12] The QBER curves for the uplink are presented without the link-budget equations or parameter values used to convert the background photon rates of Figs. 8-10 into QBER; the source rates cited in the caption (780 nm at 400 MHz, 790 nm at 100 MHz) are insufficient because receiver efficiency, telescope aperture, atmospheric transmission, detector dark counts, and any polarization misalignment all enter the calculation. The caption states that light pollution is the only noise source, which excludes detector dark counts; this should be stated explicitly in the text and the dark-count contribution quantified, otherwise the predicted sub-5% thresholds at 40 and 10 degrees cannot be reproduced.
[Section 2.2, uncertainty estimate] The total uncertainty of ±40% for the VIIRS scaling is hand-assigned from ±20% visual estimates of illuminated fractions and ±0.2% spectral scaling factors, rather than propagated from the measured distributions or from any comparison at Calgary or Priddis. Different street-lighting spectra (for example, high-pressure sodium versus LED) can change the 780/790/850 nm radiance fraction by more than the quoted 0.2% band, so the error bars in Figs. 8-10 and the thresholds in Fig. 12 are likely optimistic for QGS-UC. Replacing the visual fractions with an independent estimate, or at least adding a sensitivity analysis over a wider spectral-scaling range, is needed to support the central claim.

minor comments (5)

[Table 1] The table caption contains a typo ('T able 1') and the QGS-RAO latitude entry '51 ° 50° 52' 4.94”N' appears malformed; please correct the formatting.
[List of Abbreviations] 'Quantum Ecryption and Science Satellite' should read 'Quantum Encryption and Science Satellite'.
[Section 4, Fig. 11] The downlink QBER prediction for QGS-UW averages azimuthal measurements at each elevation, but the text does not state how many independent measurements contribute to each average or whether systematic differences between the two measurement nights were treated as uncertainties; a brief statement would help the reader interpret the error bars.
[Section 2.2, Eq. (5)] The symbols α and r_f are introduced immediately after Eq. (5), which is acceptable, but the text should also note that the rooftop radiance measurement assumes a lambertian or isotropic ground emission; this assumption is not stated in the methods section.
[Section 5, Conclusion] The conclusion that VIIRS data can 'remotely and efficiently determine the potential of a ground site' is stronger than what the single-site validation at Waterloo demonstrates; consider softening the claim to 'estimate an upper bound subject to local spectral calibration'.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the predictions rest on independent measurements and a published link model, not on fitting the target result.

full rationale

The paper's derivation chain is not circular. The downlink background rates are direct field measurements with single-photon detectors and telescopes. The uplink background estimates combine either rooftop radiance measurements or independent VIIRS DNB radiance data with a geometric conversion (Eq. 5) and a published atmospheric transmission model (Eq. 4, from Ref. [20]). The spectral scaling factors (0.7%, 0.7%, 0.5%) are measured with a spectrometer at QGS-UW, not fitted to the target QBER values, and the illuminated-area fractions in Eqs. 6-7 are visually estimated with stated uncertainties rather than optimized to reproduce the QBER curves. Applying Waterloo-derived spectral factors to Calgary and Priddis is an extrapolation that the authors explicitly flag as a source of large uncertainty, not a reduction of the prediction to its input. The QBER thresholds use link-loss models and the 5% practical limit from Refs. [20] and [26]; these are self-citations, but they are parameter-free published models and requirements with stated assumptions that do not include the present site measurements, and the paper benchmarks them against real Micius/Jinan-1 QKD experiments. No uniqueness theorem, ansatz, or renamed empirical pattern is invoked to force the result. The central claim is therefore self-contained against external data and models; any weakness lies in extrapolation and measurement transfer, not circularity.

Assumptions & free parameters 3 free parameters · 5 assumptions · 0 invented entities

The central uplink predictions depend on two visually estimated area-fraction sets, a Waterloo-only spectral scaling, and an empirical atmospheric model from the authors' prior work. The downlink conclusions rest on direct photon-counting measurements and are less parameter-dependent.

free parameters (3)

Illuminated area fraction inside VIIRS pixel = UW 1/3, UC 3/4, RAO 1/10, plus or minus 20%
Visually estimated from satellite images in Figures 3a to 3c and used in Equation 7 to convert VIIRS pixel radiance into the radiance of lit ground; this directly scales the uplink background prediction.
Illuminated area fraction inside QEYSSat footprint = UW 3/4, UC 1/2, RAO 1/10, plus or minus 20%
Visually estimated from Figures 3d to 3f to rescale the VIIRS-derived radiance to the satellite field of view; a 20% change shifts the predicted uplink counts by roughly 20%.
Spectral scaling factors for 780, 790, and 850 nm = 0.7%, 0.7%, 0.5%, plus or minus 0.2%
Measured from the spectrum around QGS-UW and applied to all three sites to convert broad-band VIIRS DNB radiance into the QEYSSat wavelength bands; site-to-site spectral differences are not characterized.

assumptions (5)

domain assumption Dark areas within the satellite footprint have zero radiance, Ldark = 0 in Equation 6.
Unlit fields and parks are assumed to contribute no uplink background, which can bias the VIIRS-derived uplink estimates downward.
domain assumption The ground acts as a uniform Lambertian emitter whose radiance measured from one rooftop direction is representative of the whole illuminated area.
Equations 2 and 5 convert a single rooftop fibre measurement into an absolute radiance and then into photons at the satellite; non-Lambertian or spatially varying ground emission would break this conversion.
domain assumption Atmospheric transmission follows eatm = 10^{-0.32 csc(theta)} from Ref. [20].
This empirical model, from a paper with overlapping authorship, is used in Equations 4 and 5 without independent validation for the specific sites and nights.
ad hoc to paper The spectral scaling factors measured at QGS-UW describe the light sources at QGS-UC and QGS-RAO.
A single local spectrum in Figure 4 is used to scale VIIRS data for all three sites; the paper notes this as a source of uncertainty but does not measure spectra at the other sites.
domain assumption QEYSSat receiver parameters such as acceptance half-angle, receiver radius, and source rates from the mission ICD are accurate.
The uplink geometry in Equation 5 and the QBER simulations use these external parameters, which are not independently verified in this paper.

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Cite this review

Pith. "Pith review of Estimating the impact of light pollution on quantum communication between QEYSSat and Canadian quantum ground station sites." pith.science (2026). https://pith.science/paper/S6HM53Y2

@misc{pith2026241214944,
  author       = {Pith},
  title        = {Pith review of: Estimating the impact of light pollution on quantum communication between QEYSSat and Canadian quantum ground station sites},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/S6HM53Y2}},
  note         = {Machine review of arXiv:2412.14944}
}

read the original abstract

Satellite to ground quantum communication typically operates at night to reduce background signals, however it remains susceptible to noise from light pollution of the night sky. In this study we compare several methodologies for determining whether a Quantum Ground Station (QGS) site is viable for exchanging quantum signals with the upcoming Quantum Encryption and Science Satellite (QEYSSat) mission. We conducted ground site characterization studies at three locations in Canada: Waterloo, Ontario, Calgary, Alberta, and Priddis, Alberta. Using different methods we estimate the background counts expected to leak into the satellite-ground quantum channel, and determined whether the noise levels could prevent a quantum key transfer. We also investigate how satellite data recorded from the Visible Infrared Imaging Radiometer Suite (VIIRS) can help estimate conditions of a particular site, and find reasonable agreement with the locally recorded data. Our results indicate that the Waterloo, Calgary, and Priddis QGS sites should allow both quantum uplinks and downlinks with QEYSSat, despite their proximity to urban centres. Furthermore, our approach allows the use of satellite borne instrument data (VIIRS) to remotely and efficiently determine the potential of a ground site.

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Pith tools

Reviewed August 11, 2026 · model on record in the stance chip above.

[1] [20]

Bourgoin, E

J. Bourgoin, E. Meyer-Scott, B. L. Higgins, B. Helou, C. Erven, H. Huebel, B. Kumar, D. Hudson, I. D’Souza, R. Girard, et al., New Journal of Physics 15, 023006 (2013)

work page 2013

[2] [1]

Korzh, C

B. Korzh, C. C. W. Lim, R. Houlmann, N. Gisin, M. J. Li, D. Nolan, B. Sanguinetti, R. Thew, and H. Zbinden, Nature Photonics 9, 163 (2015)

work page 2015

[3] [2]

Inagaki, N

T. Inagaki, N. Matsuda, O. Tadanaga, M. Asobe, and H. Takesue, Optics express 21, 23241 (2013)

work page 2013

[4] [3]

G. Avis, F. Ferreira da Silva, T. Coopmans, A. Dahlberg, H. Jirovsk´ a, D. Maier, J. Rabbie, A. Torres-Knoop, and S. Wehner, NPJ Quantum Information 9, 100 (2023)

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[5] [4]

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H.-J. Briegel, W. D¨ ur, J. I. Cirac, and P. Zoller, Physical Review Letters 81, 5932 (1998)

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work page 2017

[7] [6]

Y.-A. Chen, Q. Zhang, T.-Y. Chen, W.-Q. Cai, S.-K. Liao, J. Zhang, K. Chen, J. Yin, J.-G. Ren, Z. Chen, et al., Nature 589, 214 (2021)

work page 2021

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Jennewein, J.-P

T. Jennewein, J.-P. Bourgoin, B. Higgins, C. Holloway, E. Meyer-Scott, C. Erven, B. Heim, Z. Yan, H. Huebel, G. Weihs, E. Choi, I. D’Souza, D. Hudson, and R. Laflamme, Proceedings of SPIE, Advances in Photonics of Quantum Computing, Memory, and Communication VII 8997, 89970A (2014)

work page 2014