Resolving shortwave and longwave irradiation distributions across the human body in outdoor built environments

Ankit Joshi; Ariane Middel; Cibin T. Jose; Galina Mihaleva; Kambiz Sadeghi; Konrad Rykaczewski; Lyle Bartels; Muhammad Abdullah; Shri H. Viswanathan; Sylwester Wereski

REVIEW 3 major objections 6 minor 3 references

Resolving shortwave and longwave irradiation distributions across the human body in outdoor built environments

T0 review · 3 major / 6 minor · reviewed 2026-08-08 · deepseek-v4-flash

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Pith's one-line read This paper establishes that subtracting heat fluxes on white and tan twin zones of an outdoor thermal manikin isolates shortwave and longwave irradiation on eleven body zones, and that a radiometer-driven simulation of the manikin…

desk verdict New experimental technique for spectrally resolved body-part irradiation; the equal-irradiation assumption needs an independent check before the validation claims fully hold. read the letter →

arxiv 2502.04216 v2 pith:LB46Q7K5 submitted 2025-02-06 physics.bio-ph

Kambiz Sadeghi , Shri H. Viswanathan , Ankit Joshi , Lyle Bartels , Sylwester Wereski , Cibin T. Jose , Galina Mihaleva , Muhammad Abdullah

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Ariane Middel Konrad Rykaczewski

This is my paper · ORCID

classification physics.bio-ph

keywords outdoorradiationexchangeshortwavelongwavethermalmanikincomputationalmeanradianttemperatureclothingradiativeheatflux

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 develops and cross-validates two ways to measure how much solar (shortwave) and infrared (longwave) radiation each part of a person's body absorbs outdoors. A thermal manikin painted white on one symmetric half lets the authors subtract matched white/tan zone heat fluxes to isolate the two spectral bands zone by zone; a cheaper hybrid method feeds six-direction radiometer data into a simulated twin of the manikin. In unobstructed sun the two methods agree within about 100 W/m² on most body zones, with the largest disagreements on the hand and pelvis, and both show that longwave radiation is nearly uniform while shortwave is strongly anisotropic. The authors then use the manikin to show that shirt color substantially changes how much radiative heat reaches the skin. If the central claim holds, urban designers and clothing engineers gain per-body-part spectral irradiation data that mean radiant temperature cannot provide.

What carries the argument

The key machinery is the two-color subtraction identity (Eqs. 3 and 4): with the manikin shell held at air temperature to remove convection, the net heat flux on a white-painted zone minus that on its symmetric tan twin, divided by the difference of their shortwave absorptivities, gives the shortwave irradiation on that zone; longwave irradiation then follows from the tan-zone energy balance. The companion machinery is the conversion of six-directional MaRTy fluxes into three radiation sources—direct solar, diffuse sky, and specular ground reflection—that drive a Surface-to-Surface radiation simulation on the manikin's virtual twin. The two-color identity does the spectral separation; the source-decomposition does the mapping from a point measurement to a 3D body.

What would settle it

Measure the same sunlit manikin with a third coating color on a third symmetric zone; if the equal-irradiation premise is exact, the over-determined three-color system returns the same $S_i$ for all zone pairs, whereas any systematic difference between pairs reveals the bias the white/tan assumption introduces.

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Extended reading notes

Core claim

The central discovery is that spectrally resolved irradiation across the human body can be obtained by subtracting net heat-flux measurements from symmetric body zones that differ only in shortwave absorptivity. With convection suppressed by holding shell temperature at air temperature, the white/tan flux difference divided by the absorptivity difference yields the shortwave irradiation $S_i$ on zone $i$, and the longwave irradiation $L_i$ follows once $S_i$ is known (Eqs. 3-4). Under this two-color method, the manikin's 11 zone pairs give shortwave fluxes that a computational twin—driven by MaRTy's six-directional radiometer fluxes converted to direct, diffuse, and ground-reflected sources—reproduces in unobstructed sun to within about 100 W/m² on most zones, with hand and pelvis as exceptions. The same measurements show that longwave irradiation is uniform to within ±25 W/m² across the body, while shortwave irradiation varies strongly zone to zone, so whole-body mean radiant temperature hides the localized radiative load that the new maps resolve.

Load-bearing premise

The load-bearing premise is that the shortwave irradiation on a white zone equals that on its matching tan zone; this fails when shade or reflections vary across the body's half-width, because the white surface reflects more shortwave onto nearby tan zones and a shadow boundary can fall between the two zones.

Editorial extensions

If this is right

Shortwave irradiation on each of the 11 body zones can now be measured in real outdoor sun and shade, not just inferred from whole-body indices.
In unobstructed sun, the MaRTy-driven simulation reproduces the manikin's zone fluxes within about 100 W/m² on most zones, so the cheaper hybrid route can stand in for the manikin.
Longwave irradiation is uniform across the body in sun and shade in these conditions, so it can be treated with a single average value.
Clothing effects: a white shirt cut the whole-body upper-torso radiative load from 159 W to 73 W, with darker shirts giving less attenuation; the model predicts shirt-level fluxes within 15%.
The methods require irradiation homogeneity over about 0.5 m and instrument placement within a few meters for complex settings, so swap positions in heterogeneous canyons.
The methods require irradiation homogeneity over about 0.5 m and instrument placement within a few meters for complex settings, so positions must be swapped in heterogeneous canyons.

Reading between the lines

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

A natural extension is to add a third coating color to a third symmetric zone, making the two-color subtraction over-determined; systematic disagreement among the zone pairs would directly quantify the equal-irradiation bias the paper only estimates by simulation.
If the two methods are combined with a three-dimensional anemometer, the radiometer-driven simulation may replace the expensive manikin for routine urban heat-exposure surveys, as the paper hints but does not establish.
The methods assume longwave uniformity; near hot walls, cooling panels, or photovoltaic shade structures the longwave field will be directional, so the simulation would need a directional infrared source model rather than the average flux used here.
The clothing attenuation results suggest a testable design rule: zonal spectral irradiation maps could drive placement of reflective or emissive fabrics on the body—for example, white fabrics matter most on sun-facing zones like the front upper arm and chest—rather than choosing a single color for the whole garment.

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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

Best read as a methods paper: the two-color manikin subtraction is genuinely new and the field dataset is the first of its kind. The hybrid MaRTy-to-simulation pipeline is a natural extension of your earlier boundary-condition work, and here it gets a real outdoor test. The paper is honest about where the methods break down (partial shade, urban canyon), and the shirt attenuation results are a nice practical bonus.

The core algebra behind the two-color method is straightforward, and the absorptivity measurements are independent, so the central idea is sound. What I'd want before leaning on the quantitative claims is an uncertainty budget. The subtraction amplifies measurement noise by roughly a factor of 1.3, and no error bars or propagation are reported for the S_i values. More importantly, the equal-irradiation assumption is checked only with the same simulation pipeline that is the validation target. The stress-test note is right: the ~100 W/m2 agreement in unobstructed sun does not bound the bias from S_W ≠ S_T, especially on the inner thigh/calf where mutual reflections are largest. The paper acknowledges this and gives simulation-based estimates of 10 W/m2 typical and 30-40 W/m2 worst case, but those estimates come from the very model that misses the pelvis and hand. An independent check—say a small co-located pyranometer or a controlled lamp test with known asymmetric irradiation—would close the loop.

The hand and pelvis discrepancies are discussed physically rather than swept under the rug, and the partial-shade failures are explicitly attributed to the equal-irradiation premise. That is good scientific hygiene. The main missing pieces are data/code release, uncertainty propagation, and an independent validation of the twin-irradiation assumption. Without those, the "closely aligned in most cases" claim is more a demonstration than a proof.

The intended audience is urban climate, human biometeorology, and radiative-cooling textile researchers. This paper deserves a serious referee: the novelty is real, the limitations are acknowledged, and the field needs experimental benchmarks like this. I'd ask the authors to add uncertainty analysis and release the raw zonal flux data before publication, but this is not a desk-reject.

Referee Report

3 major / 6 minor

Summary. This paper introduces and field-tests two methods for resolving shortwave and longwave irradiation across 11 body zones of an outdoor thermal manikin. The first, 'two-color' method uses symmetric white- and tan-coated zones and Eqs. (3)-(4) to separate spectral components from net heat flux measurements after eliminating convection. The second hybrid method converts MaRTy six-directional radiometer measurements into directional, reflected, and diffuse shortwave boundary conditions for a Comsol simulation of a virtual twin of the manikin. The methods are compared in unobstructed sun, partial tree shade, full shade, and a narrow urban canyon, and the manikin is used to quantify irradiation attenuation by five long-sleeve shirts of different colors. The main reported result is that the two methods generally agree within roughly 100 W/m2 in unobstructed sun except for the pelvis and hand zones, and that longwave irradiation is nearly uniform across the body. The paper also presents a simple model for predicting the net radiative heat flux under the tested shirts.

Significance. If the measurement chain is accepted, the two-color manikin provides the first experimental, spectrally resolved irradiation distribution over body zones in outdoor conditions, which is a valuable benchmark for human-centric radiation simulations and for studying radiatively engineered textiles. The hybrid MaRTy-simulation approach is more accessible and could be widely adopted in urban climate studies. The shirt tests provide useful, quantitative data on color-dependent radiative attenuation. However, the central experimental validation currently rests in part on the same simplified simulation pipeline that is being validated, and the agreement claim is not yet supported by a formal uncertainty analysis. Strengths of the paper include the algebraic consistency of Eqs. (3)-(4), the independent spectral characterization of the coatings and fabrics, and the clearly acknowledged limitations of the methods in heterogeneous shade.

major comments (3)

[Section 3.1, Eq. (3) and Figs. 6-7] The equal-irradiation assumption S_i,T = S_i,W underlying Eq. (3) is load-bearing for the central experimental claim, yet its only quantitative check is the Comsol virtual-manikin simulation in Section 3.1. That simulation is also the target whose agreement with the manikin is being used to validate the method, so using it to bound the self-reflection bias (typically below 10 W/m2, at worst 30-40 W/m2) is circular. Because Eq. (3) propagates any true difference between the tan and white twin irradiations with a coefficient alpha_ST/(alpha_ST-alpha_SW) = 1.29, an unmeasured 30 W/m2 imbalance would produce roughly 39 W/m2 of error in S_i, comparable to the claimed agreement level. The manuscript should either provide an independent measurement of the irradiation incident on corresponding white and tan zones (for example, miniature pyranometers temporarily placed on the twins, or a coating-swap test) or explicitly re-frame the sunny-case agreement as conditional on the simulation-based correction.
[Section 3.1, Eq. (3) and Figs. 6-7] The quantitative agreement claim is not supported by an uncertainty analysis. The input heat fluxes q_i, the integrated coating absorptivities, and the shell/air temperature matching all carry uncertainties, and Eq. (3) amplifies the q-difference uncertainty by roughly 1/(alpha_ST-alpha_SW) = 1.9, with Eq. (4) adding further sensitivity. Yet Figs. 6 and 7 show no error bars or confidence intervals for the ANDI-derived fluxes, and the text describes agreement qualitatively as 'closely aligned' or 'within roughly 100 W/m2'. The authors should propagate measurement uncertainties through Eqs. (3)-(4) and report them on the time series, or at least state explicitly which error sources dominate and why they do not affect the conclusions.
[Section 4.1 and SM Fig. S13] The hand-zone discrepancy is explained by heat conduction from the uncooled fingers into the cooled palm sensor, but the claimed 'fraction' of finger-absorbed radiation reaching the palm is not quantified. Because the hand is one of only two zones that fall outside the stated agreement level, this explanation should be supported either by a thermal model with explicit conduction and emission/convection losses from the fingers or by a measurement with the fingers thermally decoupled. Without this, the hand result remains an unexplained outlier rather than a characterized limitation.

minor comments (6)

[Section 2.3, after Eq. (4)] The approximation alpha_LW = alpha_LT (0.98 vs 0.99) is stated to be acceptable, but the sensitivity of Eq. (4) to this small difference is not quantified; a one-line error estimate would help.
[Section 2.7, Eq. (13)] The convective coefficient h is fixed at 10 W/m2.C based on a mean wind speed of 1.3 m/s, but no sensitivity of the claimed 15% model agreement to h is reported; a short sensitivity range would strengthen the clothing-model result.
[Section 3.2, Fig. 8] Error bars appear only in Fig. 8b, while the other snapshot bar plots and time series in Fig. 8 and the Supplementary Material do not show the same uncertainty treatment; consistency would make the comparisons easier to interpret.
[Section 3.3 and SM Fig. S12] The choice to present the third repetition of the shirt tests rather than the average across all four repetitions is not fully justified; since the text notes that results were comparable, reporting a pooled estimate or all four repetitions would be more transparent.
[Section 2.5, Eq. (9)] The Haurwitz comparison uses assumed values kt = 0.8 and kd = 0.2 without independent measurement; this is acceptable for a sanity check, but the model-assumption status should be stated more explicitly in the main text.
[Throughout] There are several minor typographical and wording issues, for example 'the air measurement value' in Section 2.3 should read 'the measured air temperature', and the sentence beginning 'It is worthwhile pointing out even that' in Section 2.5 is grammatically incomplete.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the two-color manikin equations are an algebraic spectral separation from independently measured heat fluxes and absorptivities, and the simulation comparison uses MaRTy radiometer inputs, not manikin-derived outputs.

full rationale

Walking the derivation chain, the two-color manikin method in Section 2.3 uses independent energy balances for tan and white zones (Eqs. 1-2), then solves for shortwave and longwave irradiation via exact algebraic rearrangement (Eqs. 3-4) under explicitly stated assumptions about equal irradiation and equal longwave absorptivity. The absorptivities are measured spectroscopically or taken from prior calibration, and the measured heat fluxes are not fitted parameters. The hybrid MaRTy-simulation method builds its boundary conditions from six-direction radiometer measurements (Eqs. 5-8) and the manikin geometry, not from the two-color manikin's zonal outputs, so the subsequent agreement between the two methods is an independent cross-check rather than a reduction to inputs. The paper's reliance on the authors' earlier ANDI and radiation-simulation work supplies instrumentation and modeling infrastructure, but the present experiments validate those methods against physically separate measurements. The acknowledged equal-irradiation assumption is assessed numerically with a radiative simulation whose inputs also do not include the two-color results; that is a model-based uncertainty estimate rather than definitional circularity, though it is not an independent empirical bound. No fitted parameter is renamed a prediction, no uniqueness theorem is imported, and no equation reduces to its own target. The skeptical concern about shared model assumptions is a validation or uncertainty limitation, not a circular derivation.

Assumptions & free parameters 4 free parameters · 6 assumptions · 0 invented entities

The central methods rest on measured spectral absorptivities and a symmetry assumption rather than a fitted parameter set. The main free inputs are an assumed convection coefficient for the clothing model, clear-sky constants used only for comparison, and a modeling choice for constant reflectivity. No new physical entities are introduced.

free parameters (4)

heat transfer coefficient h for shirt model = 10 W·m^-2·°C^-1
Chosen in Section 3.4 as representative of measured wind speed 1.3±0.8 m/s; not fitted to shirt data, but it affects the model predictions for fabric temperature and heat flux.
clearness index kt = 0.8
Assumed from prior references in Section 2.5 for the Haurwitz global solar radiation model; used only for comparison, not for the central manikin measurements.
diffuse fraction kd = 0.2
Assumed from prior references in Section 2.5 to split Haurwitz global radiation into diffuse and direct components; not fitted here.
constant directional reflectivity rho = 0.16
Calculated from Eq. 7, with a constant 0.16 variant used in Eq. 8 for high solar zenith angles; the choice between constant and varying rho affects late-afternoon direct shortwave values.

assumptions (6)

domain assumption Irradiation on symmetric white and tan zones is equal
Section 2.3, Eq. 3-4; this breaks under partially shaded or cm-scale heterogeneous radiation, as acknowledged in Section 4.2 for the Palo Verde tree shade.
domain assumption Longwave absorptivities of white and tan coatings are equal (0.98 vs 0.99)
Section 2.3; the small difference introduces a small error in Eq. 3-4, but the analysis treats them as identical.
domain assumption Convection is eliminated by setting manikin shell temperature equal to air temperature
Section 2.3; this requires stable air temperature and was conducted during afternoons. Residual temperature mismatch would add an unmodeled convective term to Eq. 1-2.
domain assumption Diffuse shortwave irradiation equals the minimum of the four vertical MaRTy sensors, and excess ground reflection is a specular direct component
Section 2.5, Eq. 5-7; this is inaccurate in complex shade or narrow canyons where the diffuse field is anisotropic over small distances.
domain assumption Haurwitz model with kt=0.8 and kd=0.2 describes local clear-sky solar radiation
Section 2.5, Eq. 9, used for comparison with transformed MaRTy fluxes; values are taken from prior work and not fitted in this paper.
domain assumption Longwave irradiation is uniform across the manikin and equal to the average of MaRTy six-directional fluxes
Section 2.6 and Conclusions; supported by the measured longwave uniformity in the tested sites, but the authors note it may fail near heated walls or cooling panels.

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Cite this review

Pith. "Pith review of Resolving shortwave and longwave irradiation distributions across the human body in outdoor built environments." pith.science (2026). https://pith.science/paper/LB46Q7K5

@misc{pith2026250204216,
  author       = {Pith},
  title        = {Pith review of: Resolving shortwave and longwave irradiation distributions across the human body in outdoor built environments},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/LB46Q7K5}},
  note         = {Machine review of arXiv:2502.04216}
}

read the original abstract

Outdoor built environments can be designed to enhance thermal comfort, yet the relationship between the two is often assessed in whole-body terms, overlooking the asymmetric nature of thermal interactions between the human body and its surroundings. Moreover, the radiative component of heat exchange-dominant in hot and dry climates-is typically lumped into a single artificial metric, the mean radiant temperature, rather than being resolved into its shortwave and longwave spectral components. The shortwave irradiation distribution on the human body is often highly anisotropic, causing localized thermal discomfort in outdoor environments. However, no existing methods effectively quantify shortwave and longwave irradiation distributions on the human body. To address this gap, we developed two methods to quantify these processes. The first approach uses an outdoor thermal manikin with a white-coated side, enabling the separation of spectral components by subtracting measurements from symmetrically corresponding surface zones of tan color. The second hybrid approach converts radiometer measurements in six directions into boundary conditions for computational thermal manikin simulations. We evaluated irradiation distributions for various body parts using both methods during outdoor measurements across sunny, partially shaded, and fully shaded sites under warm to extremely hot conditions. In most cases, the two methods produced closely aligned results, with divergences highlighting their respective strengths and limitations. Additionally, we used the manikin to quantify irradiation attenuation provided by five long-sleeve shirts with colors ranging from white to black. These advanced methods can be integrated with airflow and thermoregulatory modeling to optimize outdoor built environments for enhanced human thermal comfort.

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Reference graph

Works this paper leans on

3 extracted references · 3 canonical work pages

[1]

Rykaczewski, A

K. Rykaczewski, A. Joshi, S.H. Viswanathan, S.S. Guddanti, K. Sadeghi, M. Gupta, A.K. Jaiswal, K. Kompally, G. Pathikonda, R. Barlett, J.K. Vanos, A. Middel, A simple three-cylinder radiometer and low-speed anemometer to characterize human extreme heat exposure, Int J Biometeorol 68 (2024) 1081–1092

work page 2024
[2]

ASTM F1291-16, Standard Test Method for Measuring the Thermal Insulation of Clothing Using a Heated Manikin, American Society for Testing and Materials Book of Standards 11 (2004) 1–7

work page 2004
[3]

Holmer, F

B. Holmer, F . Lindberg, D. Rayner, S. Thorsson, How to transform the standing man from a box to a cylinder–a modified methodology to calculate mean radiant temperature in field studies and models, in: Proceedings of the 9th International Conference on Urban Climate (ICUC9), Toulouse, France, 2015: pp. 20–24

work page 2015

Pith tools

Reviewed August 8, 2026 · model on record in the stance chip above.

[1] [1]

Rykaczewski, A

K. Rykaczewski, A. Joshi, S.H. Viswanathan, S.S. Guddanti, K. Sadeghi, M. Gupta, A.K. Jaiswal, K. Kompally, G. Pathikonda, R. Barlett, J.K. Vanos, A. Middel, A simple three-cylinder radiometer and low-speed anemometer to characterize human extreme heat exposure, Int J Biometeorol 68 (2024) 1081–1092

work page 2024

[2] [2]

ASTM F1291-16, Standard Test Method for Measuring the Thermal Insulation of Clothing Using a Heated Manikin, American Society for Testing and Materials Book of Standards 11 (2004) 1–7

work page 2004

[3] [3]

Holmer, F

B. Holmer, F . Lindberg, D. Rayner, S. Thorsson, How to transform the standing man from a box to a cylinder–a modified methodology to calculate mean radiant temperature in field studies and models, in: Proceedings of the 9th International Conference on Urban Climate (ICUC9), Toulouse, France, 2015: pp. 20–24

work page 2015