Lava flow surface roughness and depolarized radar scattering

Abstract

Abstract. Surface roughness has a strong controlling influence on radar scattering and other types of remote sensing observations. We compare field measurements of surface topography and dielectric constant for a range of lava flow textures to aircraft multipolarization radar observations at 5.7. 24, and 68 cm (C, L, and P band) wavelengths. The roughness is found to vary with scale in a self-affine (fractal) manner for scale lengths between 25 cm (the smallest horizontal step size) and 3-5 m. This result is used to demonstrate that a two-component surface description, consisting of the fractal dimension and rms height or slope at some reference scale, can resolve some of the ambiguities in previous efforts to quantify roughness. At all three radar wavelengths, the HV backscatter cross section is found to vary in an approximately exponential fashion with the rms height or Allan deviation at some reference scale, up to a saturation point, where the surface appears entirely diffusely scattering to the radar. Based on these observations, we use a parameter, y, defined as the ratio of rms height to the particular scale of measurement. Backscatter values at 24-cm wavelength and the topographic profile data were used to derive expressions which link the HV radar cross section to 7 or to the analogous wavelength-scale rms slope. These equations provide a reasonable fit to 24-and 68-cm echoes and for rough surfaces at 5.7 cm, but yield poor results for 5.7-cm echoes on smooth terrain. We conclude that the roughness at the two larger scales is well described by a single fractal dimension and rms height, but that texture at very srnall scales is characterized by different statistics. This inference is supported by analysis of 5-cm horizontal spacing topographic profiles, 'i'he relationships defined here allow determination of the surface rms height or slope at the scale of the radar wavelength. Given radar data at additional wavelengths, a more complete view of the statistical properties of the surface can be developed. Such techniques may be useful in analyses of synthetic aperture radar images for terrestrial volcanic areas, Magellan data for Venus, and other planetary radar observations. Introductionsurface roughness and specific remote sensing properties for many types of observations remains elusive. In this paper, we Tlie topography of natura! surfaces at scales of a icw meters focus on the nature of roughness and its scale dependence for or less is commonly referred to as roughness. These variations terrestrial rwcky lava surfaces, and the effect of such changes in height and slope, their magnitude, and the changes in on depolarized radar backscatter at a variety of incidence structure as a function of scale length are of fundamental ai\gies and wavelengths. importance to the interpretation of geologic emplacement Analysis of radar scattering from natural surfaces has been mechanisms and subsequent modification. For most planetary of interest for over 30 years, and two distinct approaches have studies and many terr...

The unique radar properties of silicic lava domes

“…Shepard et al [1995] and Campbell and Shepard [1996]). Table 2 summarizes the topographic parameters for the 83 transects measured.…”

“…Interpretation of data from planetary missions requires an understanding of related phenomena on Earth, a task that often includes a search for appropriate terrestrial analogues to planetary features. The Magellan radar mapping mission to Venus revealed a variety of volcanic features, and the interpretation of the radar images inspired a number of studies utilizing radar remote sensing of terrestrial volcanoes and lava flows [e.g., Greeley and Martel, 1988;Ford et al, 1989;Gaddis et al, 1989Gaddis et al, , 1990Campbell and Campbell, 1992;Arvidson et al, 1993;Mouginis-Mark, 1995;Campbell and Shepard, 1996]. A remarkable finding from Magellan was a class of apparently volcanic landforms referred to as ''steep-sided'' or ''pancake'' domes Pavri et al, 1992;McKenzie et al, 1992;Fink et al, 1993;Bridges, 1997;Stofan et al, 2000].…”

Scale-Dependent Surface Roughness Behavior and Its Impact on Empirical Models for Radar Backscatter

“…Given these results. Campbell and Shepard [17] proposed that scattering from self-affine terrain be described as a function of the wavelength-scaled rms height, 7, or rms slope s(A).…”

Impact of Environmental Factors on the Spectral Characteristics of Lava Surfaces: Field Spectrometry of Basaltic Lava Flows on Tenerife, Canary Islands, Spain

“…Surface roughness defined by the micro-topographic variations is an important characteristic of lava surfaces, controlled by its emplacement dynamics (e.g., [18,19,43]). Roughness controls the lava surface porosity and will therefore influence the type and rate of surface weathering [44,45].…”

“…Improving the understanding of the spectra of lava surfaces has the potential to help to better interpret the spectra of volcanic areas recorded on satellite images and, therefore, to facilitate the realization of our long-term goals, i.e., mapping and dating lava flows. Whereas several studies have investigated the factors controlling the contrasted characteristics of lava in the thermal infrared and radar wavelength ranges [14,[17][18][19], only limited attention has been dedicated to unravelling the factors controlling the large spectral contrasts observed within lava flow fields in the visible to near-infrared range. There is therefore a need to build a spectral library of lava surfaces, to find out how they behave spectrally, to characterize how this spectral behavior varies in space and time and to investigate which flow characteristics or environmental factors influence these variations.…”