Simulating optical top-of-atmosphere radiance satellite images over snow-covered rugged terrain

Lamare, Maxim; Dumont, Marie; Picard, Ghislain; Larue, Fanny; Tuzet, François; Delcourt, Clément; Arnaud, Laurent

doi:10.5194/tc-14-3995-2020

Cited by 20 publications

(18 citation statements)

References 91 publications

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“…Nevertheless, other authors have drawn different conclusions regarding the role of re-illumination in the same study area. Lamare et al (2020) found a significant contribution of multiple reflections on the simulated top-ofatmosphere (TOA) radiance in the same area as ours. A hypothesis to explain this discrepancy is the dependence on the sun's position and the configuration of the terrain.…”

Section: Role Of the Topographic Effectssupporting

confidence: 77%

Modelling surface temperature and radiation budget of snow-covered complex terrain

et al. 2022

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Abstract. The surface temperature controls the temporal evolution of the snowpack, playing a key role in metamorphism and snowmelt. It shows large spatial variations in mountainous areas because the surface energy budget is affected by the topography, for instance because of the modulation of the short-wave irradiance by the local slope and the shadows and the short-wave and long-wave re-illumination of the surface from surrounding slopes. These topographic effects are often neglected in large-scale models considering the surface to be flat and smooth. Here we aim at estimating the surface temperature of snow-covered mountainous terrain in clear-sky conditions in order to evaluate the relative importance of the different processes that control the spatial variations. For this, a modelling chain is implemented to compute the surface temperature in a kilometre-wide area from local radiometric and meteorological measurements at a single station. The first component of this chain is the Rough Surface Ray-Tracing (RSRT) model. Based on a photon transport Monte Carlo algorithm, this model quantifies the incident and reflected short-wave radiation on every facet of the mesh describing the snow-covered terrain. The second component is a surface scheme that estimates the terms of the surface energy budget from which the surface temperature is eventually estimated. To assess the modelling chain performance, we use in situ measurements of surface temperature and satellite thermal observations (Landsat 8) in the Col du Lautaret area, in the French Alps. The results of the simulations show (i) an agreement between the simulated and measured surface temperature at the station for a diurnal cycle in winter within 0.2 ∘C; (ii) that the spatial variations in surface temperature are on the order of 5 to 10 ∘C in the domain and are well represented by the model; and (iii) that the topographic effects ranked by importance are the modulation of solar irradiance by the local slope, followed by the altitudinal variations in air temperature (lapse rate), the re-illumination by long-wave thermal emission from surrounding terrain, and the spectral dependence of snow albedo. The changes in the downward long-wave flux because of variations in altitude and the absorption enhancement due to multiple bounces of photons in steep terrain play a less significant role. These results show the necessity of considering the topography to correctly assess the energy budget and the surface temperature of snow-covered complex terrain.

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Section: Role Of the Topographic Effectssupporting

confidence: 77%

Modelling surface temperature and radiation budget of snow-covered complex terrain

et al. 2022

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Section: Role Of the Topographic Effectsmentioning

confidence: 86%

“…Nevertheless, even if the literature for the smaller scales -that of the ripples, dunes, sastrugi and penitents -is usually distinct and scarcer, the principles equally apply to all the scales because the radiative transfers between faces are invariant by scale change. The exception is over long distances when the atmospheric scattering and absorption effects due to the air present between the terrain faces become significant (Lamare et al, 2020). https://doi.org/10.5194/tc-2021-180 Preprint.…”

Section: Introductionmentioning

confidence: 99%

Modelling surface temperature and radiation budget of snow-covered complex terrain

Robledano

Picard

Arnaud

et al. 2021

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Abstract. The surface temperature controls the temporal evolution of the snowpack playing a key role in many physical processes such as metamorphism, snowmelt, etc. It shows large spatial variations in mountainous areas because the surface energy budget is affected by specific radiative processes that occur due to the topography, such as the modulation of the irradiance by the local slope, the shadows and the re-illumination of the surface from surrounding slopes. These topographic effects are often neglected in large scale models considering the surface as flat and smooth. Here we aim at estimating the surface temperature and the energy budget of snow-covered complex terrains, in order to evaluate the relative importance of the different processes that control the spatial variations. For this, a modelling chain is implemented to derive surface temperature in a kilometre-wide area from local radiometric and meteorological measurements at a single station. The main component is the Rough Surface Ray-Tracing (RSRT) model, based on a photon transport Monte Carlo algorithm to quantify the incident and reflected radiation on every facet of a mesh, describing the snow-covered surface. RSRT is coupled to a surface scheme in order to estimate the complete energy budget from which the surface temperature is solved. To assess the modelling chain performance, we use in situ measurements of surface temperature and satellite thermal observations (TIRS sensor aboard Landsat-8) in the Col du Lautaret area, in the French Alps. The satellite images are corrected from atmospheric effects with a single-channel algorithm. The results of the simulation show (i) an agreement between the simulated and observed surface temperature at the station for a diurnal cycle in winter within 0.3 °C; (ii) the spatial variations of surface temperature are on the order of 5 to 10 °C between opposed slope orientations and are well represented by the model; (iii) the importance of the considered topographic effects is up to 1 °C, the most important being the modulation of solar irradiance by the topography, followed by altitudinal variations in air temperature, long-wave thermal emission from surrounding terrain, spectral dependence of snow albedo, and absorption enhancement due to multiple bounces of photons in steep terrain. These results show the necessity of considering the topography to correctly assess the energy budget and the surface temperature of snow-covered complex terrain.

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“…Atmospheric and radiometric slope effect corrections over mountainous areas are necessary for state-of-the-art preprocessing in optical remote sensing [53,54]. This postprocessing is essential for surface albedo retrieval in rugged terrain, particularly for glaciers and snow-covered areas [55][56][57][58]. We analyze the performance of two approaches to correct the differential solar illumination effects: (1) the cosine correction taking into account only the direct illumination (lambertian case) (Figure 2) [59,60]; and (2) the Gamma correction, more complex, considering both direct and diffuse illuminations (non-Lambertian case) [18].…”

Section: In-situ Measurementsmentioning

confidence: 99%

Processing of VENµS Images of High Mountains: A Case Study for Cryospheric and Hydro-Climatic Applications in the Everest Region (Nepal)

et al. 2022

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In the Central Himalayas, glaciers and snowmelt play an important hydrological role, as they ensure the availability of surface water outside the monsoon period. To compensate for the lack of field measurements in glaciology and hydrology, high temporal and spatial resolution optical remotely sensed data are necessary. The French–Israeli VENµS Earth observation mission has been able to complement field measurements since 2017. The aim of this paper is to evaluate the performance of different reflectance products over the Everest region for constraining the energy balance of glaciers and for cloud and snow cover mapping applied to hydrology. Firstly, the results indicate that a complete radiometric correction of slope effects such as the Gamma one (direct and diffuse illumination) provides better temporal and statistical metrics (R2 = 0.73 and RMSE = 0.11) versus ground albedo datasets than a single cosine correction, even processed under a fine-resolution digital elevation model (DEM). Secondly, a mixed spectral-textural approach on the VENµS images strongly improves the cloud mapping by 15% compared with a spectral mask thresholding process. These findings will improve the accuracy of snow cover mapping over the watershed areas downstream of the Everest region.

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Simulating optical top-of-atmosphere radiance satellite images over snow-covered rugged terrain

Cited by 20 publications

References 91 publications

Modelling surface temperature and radiation budget of snow-covered complex terrain

Modelling surface temperature and radiation budget of snow-covered complex terrain

Modelling surface temperature and radiation budget of snow-covered complex terrain

Processing of VENµS Images of High Mountains: A Case Study for Cryospheric and Hydro-Climatic Applications in the Everest Region (Nepal)

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