A universal approach for drainage basins

Drainage basins are essential to Geohydrology and Biodiversity. Defining those regions in a simple, robust and efficient way is a constant challenge in Earth Science. Here, we introduce a model to delineate multiple drainage basins through an extension of the Invasion Percolation-Based Algorithm (IPBA). In order to prove the potential of our approach, we apply it to real and artificial datasets. We observe that the perimeter and area distributions of basins and anti-basins display long tails extending over several orders of magnitude and following approximately power-law behaviors. Moreover, the exponents of these power laws depend on spatial correlations and are invariant under the landscape orientation, not only for terrestrial, but lunar and martian landscapes. The terrestrial and martian results are statistically identical, which suggests that a hypothetical martian river would present similarity to the terrestrial rivers. Finally, we propose a theoretical value for the Hack's exponent based on the fractal dimension of watersheds, $\gamma=D/2$. We measure $\gamma=0.54 \pm 0.01$ for Earth, which is close to our estimation of $\gamma \approx 0.55$. Our study suggests that Hack's law can have its origin purely in the maximum and minimum lines of the landscapes.Comment: 20 pages, 6 Figures, and 1 Tabl

Radar sounding using the Cassini altimeter waveform modeling and Monte Carlo approach for data inversion observations of Titan's seas

Recently, the Cassini RADAR has been used as a sounder to probe the depth and constrain the composition of hydrocarbon seas on Saturn's largest moon, Titan. Altimetry waveforms from observations over the seas are generally composed of two main reflections: the first from the surface of the liquid and the second from the seafloor. The time interval between these two peaks is a measure of sea depth, and the attenuation from the propagation through the liquid is a measure of the dielectric properties, which is a sensitive property of liquid composition. Radar measurements are affected by uncertainties that can include saturation effects, possible receiver distortion, and processing artifacts, in addition to thermal noise and speckle. To rigorously treat these problems, we simulate the Ku-band altimetry echo received from Titan's seas using a two-layer model, where the surface is represented by a specular reflection and the seafloor is modeled using a facet-based synthetic surface. The simulation accounts for the thermal noise, speckle, analog-to-digital conversion, and block adaptive quantization and allows for possible receiver saturation. We use a Monte Carlo method to compare simulated and observed waveforms and retrieve the probability distributions of depth, surface/subsurface intensity ratio, and subsurface roughness for the individual double-peaked waveform of Ligeia Mare acquired by the Cassini spacecraft in May 2013. This new analysis provides an update to the Ku-band attenuation and results in a new estimate for its loss tangent and composition. We also demonstrate the ability to retrieve bathymetric information from saturated altimetry echoes acquired over Ontario Lacus in December 2008

Topography of (exo)planets

Current technology is not able to map the topography of rocky exoplanets, simply because the objects are too faint and far away to resolve them. Nevertheless, indirect effect of topography should be soon observable thanks to photometry techniques, and the possibility of detecting specular reflections. In addition, topography may have a strong effect on Earth-like exoplanet climates because oceans and mountains affect the distribution of clouds \citep{Houze2012}. Also topography is critical for evaluating surface habitability \citep{Dohm2015}. We propose here a general statistical theory to describe and generate realistic synthetic topographies of rocky exoplanetary bodies. In the solar system, we have examined the best-known bodies: the Earth, Moon, Mars and Mercury. It turns out that despite their differences, they all can be described by multifractral statistics, although with different parameters. Assuming that this property is universal, we propose here a model to simulate 2D spherical random field that mimics a rocky planetary body in a stellar system. We also propose to apply this model to estimate the statistics of oceans and continents to help to better assess the habitability of distant worlds

Simulated recovery of Europa's global shape and tidal Love numbers from altimetry and radio tracking during a dedicated flyby tour

The fundamental scientific objectives for future spacecraft exploration of Jupiter's moon Europa include confirmation of the existence of subsurface ocean beneath the surface ice shell and constraints on the physical properties of the ocean. Here we conduct a comprehensive simulation of a multiple-flyby mission. We demonstrate that radio tracking data can provide an estimate of the gravitational tidal Love number k2 with sufficient precision to confirm the presence of a liquid layer. We further show that a capable long-range laser altimeter can improve determination of the spacecraft position, improve the k2 determination (2 (3-4% error), which is directly related to the amplitude of the surface tidal deformation. These measurements, in addition to the global shape accurately constrained by the long altimetric profiles, can yield further constraints on the interior structure of Europa. Key Points A multiple-flyby mission to Europa can recover key geophysical parameters Laser altimetry can uniquely and accurately recover the global shape of Europa Laser altimetry enables the recovery of h2 to constrain the ice shell thicknes

Analytical Modeling and Performance Assessment of Micropulse Photon-counting Lidar System

The melting of polar ice sheets and evidence of global warming continue to remain prominent research interests among scientists. To better understand global volumetric change of ice sheets, NASA intends to launch Ice, Cloud and land Elevation Satellite-2 (ICESat-2) in 2017. ICESat-2 employs a high frequency photon-counting laser altimeter, which will provide significantly greater spatial sampling. However, the combined effects of sub-beam complex surfaces, as well as system effects on returning photon distribution have not been systematically studied. To better understand the effects of various system attributes and to help improve the theory behind lidar sensing of complex surfaces, an analytical model using a first principles 3-D Monte Carlo approach is developed to predict system performance. Based on the latest ICESat-2 design, this analytical model simulates photons which propagate from the laser transmitter to the scene, and reflected to the detector model. A radiometric model is also applied in the synthetic scene. Such an approach allows the study of surface elevation retrieval accuracy for landscapes, as well as surface reflectivities. It was found that ICESat-2 will have a higher precision on a smoother surface, and a surface with smaller diffuse albedo will on average result in smaller bias. Furthermore, an adaptive density-based algorithm is developed to detect the surface returns without any geometrical knowledge. This proposed approach is implemented using the aforementioned simulated data set, as well as airborne laser altimeter measurement. Qualitative and quantitative results are presented to show that smaller laser footprint, smoother surface, and lower noise rate will improve accuracy of ground height estimation. Meanwhile, reasonable detection accuracy can also be achieved in estimating both ground and canopy returns for data generated using Digital Imaging and Remote Sensing Image Generation (DIRSIG) model. This proposed approach was found to be generally applicable for surface and canopy finding from photon-counting laser altimeter data

CHARAKTER SYGNAŁÓW RADIOWYCH I UTRUDNIEŃ W SYSTEMACH NAWIGACJI W BEZZAŁOGOWYCH STATKACH POWIETRZNYCH

The article dwells upon the peculiarities of radio signals concerning the use of remote-piloted vehicles. It is highlighted that it is important take into consideration the fractal analysis of remote-piloted vehicles based on diverse fractal dimensions. The significance of remote-piloted vehicle control system investigation based on radio signals is presented. Also it is highlighted that there are many hindrances during the remote-piloted vehicle flight and it is important to take them into consideration and develop methods in order to omit them. Also the vital role of remote-piloted vehicles in different spheres of life, for example, in environment research is depicted.W artykule został poruszony temat cech sygnałów radiowych w przypadku ich zastosowania w bezzałogowych statkach powietrznych. W pracy podkreśla się istotność bazowania na fraktalnych wymiarach podczas analizy fraktalnej bezzałogowych statków powietrznych. Podkreślono znaczenie sygnałów radiowych w systemach sterowania. Przedstawiono istnienie wielu utrudnień podczas lotów bezzałogowych statków powietrznych oraz wskazano na konieczność uwzględniania i opracowania metod uniknięcia tych utrudnień. Podkreślono również istotną rolę bezzałogowych statków powietrznych w różnych sferach życia, na przykład w badaniach środowiska