Spectral reflectance measurements of snow and snow covered objects: experimental studies compared with mathematical models

Selj, Gorm Krogh; Mikkelsen, Alexander

doi:10.1117/12.2597953

Cited by 3 publications

(8 citation statements)

References 26 publications

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“…At selected wavelengths between 500-2200 nm, the measured reflectance of the sand layer samples were fitted to a mathematical model, known from previous studies as the extinction model [10][11][12]15]. The model treats the sample layers as stacked (thin) plates with wavelength-dependent reflectivity and energy loss.…”

Section: Discussionmentioning

confidence: 99%

“…The extinction model has been used in recent studies to model the light reflectance and transmittance from thin and layered samles as a function of layer thickness (given by the layer mass/area) [9][10][11][12]. Wilhelm [15] derived the extinction model to describe quantitatively the reflectance, transmittance, and absorptance in terms of specific reflection and absorption characteristics of fibers.…”

Section: 1mentioning

confidence: 99%

“…We selected eight test wavelengths over a range from 550 nm to 2200 nm to carry out a preliminary test of the model fit to the data. We fitted the data by adjusting two fitting parameters: the reflectivity (𝛼) and extinction coefficient (k), following the approach used in other studies [10][11][12]. The 8 wavelengths were chosen based on the reflectance curves of the sand layers (Fig.…”

Section: Fitting the Extinction Model To The Reflectance Datamentioning

confidence: 99%

“…The wavelength distribution and amount of incoming light transmitted through a sand layer will affect the signature that any optical sensor will capture. It is also of interest to compare the light transparencies of various layer-like materials found in nature [9][10][11][12][13][14], to gain more knowledge on how much light different materials will reflect, transmit and absorb as a function of wavelength and thickness. It has already been reported on optical similarities between soil-materials and snow when they have been studied on length scales much larger than the wavelength [13].…”

Section: Introductionmentioning

confidence: 99%

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Spectral reflectance properties of sand layers covering an underlying target: experimental measurements and mathematical modelling

Selj,

Mikkelsen

2023

Target and Background Signatures IX

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Adapting to natural backgrounds is important, yet very difficult, to achieve effective camouflage. One interesting aspect is the optical depth of biomaterials as a function of both geographical region, in which the biomaterials exist, and wavelength. The effective optical thickness of sand, for instance, will vary from scene to scene, and the amount of light that is reflected and transmitted is lower in the visible wavelength region than in the near-infrared region. Such variations in optical properties should be accounted for to ensure that synthetic camouflage material has high adaption to natural backgrounds over a large set of natural scenes as well as over a large range of wavelengths. The aim with this study has been to study optical reflectance properties of thin sand layers as a function of their thickness, given in weight per area. Sand is a biomaterial abundant in many parts of the world and relevant for many camouflage purposes. In specific, we have studied spectral reflectance (350--2500 nm) of 1-6 layers of sand covering a generic target object with known spectral signature. We also present mathematical models aiming to be able to estimate the reflectance of the sand layer samples, for a given layer thickness. The models are easy to use and we show that the models are able to reproduce the spectral reflectance properties of the sand samples. The model also allows for an estimation of the optical extinction coefficient as a function of wavelength and for a given sand type. This opens for a further estimation of transmittance and absorptance of the sand layers based on the experimental reflectance data, and we explore this in the paper. We also explore how the model is able to capture optical properties of sand and compare with corresponding optical properties of other natural materials, often found in thin layers, such as leaves and snow. We think our results will be a valuable contribution to developing multi-layered camouflage material that accounts for the variation of optical depth.

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Section: Discussionmentioning

confidence: 99%

Section: 1mentioning

confidence: 99%

Section: Fitting the Extinction Model To The Reflectance Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spectral reflectance properties of sand layers covering an underlying target: experimental measurements and mathematical modelling

Selj,

Mikkelsen

2023

Target and Background Signatures IX

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“…Effective camouflage can be achieved through spectral reflectance matching and spatial fitting to the background characteristics, reducing the contrast between the camouflage and the local background [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Camouflage and nature must reflect light similarly over the entire wavelength region where electro-optical sensor threats operate [19][20][21][22]. Spatial fitting of camouflage to natural backgrounds can be achieved through frequency and orientation matching to resemble the spatial "pattern"-fingerprints of natural backgrounds, without making exact copies of a particular microhabitat [17,[23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Camouflage performance of winter uniforms: photosimulations in the visual spectrum

Mikkelsen,

Selj,

Nielsen

2023

Target and Background Signatures IX

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Minimizing electro-optical signatures of soldiers against modern sensors is a challenging task, but a task with high importance and benefits for operative soldiers that need to stay undetected. Optimizing camouflage uniforms for winter conditions efficiently reduces soldier signatures in winter scenes, especially in the visual spectrum. Snow usually dominates winter scenes and is difficult to mimic because the spectral properties of snow change with several parameters such as grain size, structure, and wetness. Developing efficient winter camouflage thus requires knowledge and data on the spectral properties of snow. This paper presents spectral data on common snow types in Norway and evaluates the camouflage performance of several winter uniforms of different colors and patterns. We assessed and ranked the camouflage performance of the uniforms quantitatively in the visible spectrum using an observer-based photosimulation where many soldiers searched for targets in various Norwegian winter scenes. By collecting a large number of detection times, indicating how difficult it was for an observer to detect each camouflage in each of the unique winter scenes, it was possible to rank the camouflage targets quantitatively. The results show how each camouflage performed (given by time of detection or as a percentage) compared to all the other camouflages in the test for each scene. The photosimulation method is time-consuming, but it gives a realistic estimation of camouflage performance over the different scenes. We discuss the performance of the various winter camouflages with their pattern and similarity to snow (color coordinates).

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Environmentally Induced Snow Transmittance Variations in the Photosynthetic Spectral Domain: Photobiological Implications for Subnivean Vegetation under Climate Warming Conditions

Baranoski,

Varsa

2024

Remote Sensing

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Variations in the productivity of subnivean vegetation can substantially affect the ecology of regions more susceptible to increasing warming levels and lead to significant feedback effects on the global climate. Due to its importance, this topic is at the center of a broad scope of interdisciplinary studies supported by field and remote sensing observations. However, the current knowledge about environmental factors affecting the penetration of photosynthetically active radiation (PAR) through snow is still constrained by the paucity of transmittance data. In this work, we aim to further the understanding about these interconnected processes. We conduct a systematic investigation about the effects of independent and combined changes in key nivological characteristics, namely thickness, saturation, density and grain size, on snow transmittance in the photosynthetic spectral domain. Our investigation is carried out through controlled in silico (computational) experiments supported by measured radiometric data. Its outcomes unveil fundamental quantitative and qualitative trends related to the role played by these nivological characteristics on the spectral quality of transmitted PAR, which is quantified in terms of red to blue (R/B), red to far-red (R/FR) and blue to far-red (B/FR) ratios. These trends include increases in the R/B ratio as well as decreases in the R/FR and B/FR ratios following thickness reductions or grain size increases, with opposite variations in these ratios being observed for saturation or density increases. Accordingly, the pairing of our findings with in situ and remotely collected information contributes to cement the scientific foundation required for the effective assessment of cause-effect loops linking accentuated vegetation greening to accelerated rates of snow cover recession.

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Spectral reflectance measurements of snow and snow covered objects: experimental studies compared with mathematical models

Cited by 3 publications

References 26 publications

Spectral reflectance properties of sand layers covering an underlying target: experimental measurements and mathematical modelling

Spectral reflectance properties of sand layers covering an underlying target: experimental measurements and mathematical modelling

Camouflage performance of winter uniforms: photosimulations in the visual spectrum

Environmentally Induced Snow Transmittance Variations in the Photosynthetic Spectral Domain: Photobiological Implications for Subnivean Vegetation under Climate Warming Conditions

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