Topography of the lunar poles from radar interferometry: a survey of cold trap locations.
Detailed topographic maps of the lunar poles have been obtained by Earth-based radar interferometry with the 3.5-centimeter wavelength Goldstone Solar System Radar. The interferometer provided maps 300 kilometers by 1000 kilometers of both polar regions at 150-meter spatial resolution and 50-meter height resolution. Using ray tracing, these digital elevation models were used to locate regions that are in permanent shadow from solar illumination and may harbor ice deposits. Estimates of the total extent of shadowed areas poleward of 87.5 degrees latitude are 1030 and 2550 square kilometers for the north and south poles, respectively. (+info)
Harmonic oscillatory orientation relative to the wind in nocturnal roosting flights of the swift Apus apus.
Swifts regularly spend the night flying at high altitude. From previous studies based on tracking radar observations, we know that they stay airborne during the night and prefer to orient themselves into the wind direction with an increased angular concentration with increasing wind speed. In this study, we investigated the orientation relative to the wind of individual swifts by frequency (discrete Fourier transform) and autocorrelation analysis based on time series (10s intervals) of the angle between the swifts' heading and the wind direction for radar trackings of long duration (9-60 min). The swifts often showed a significant harmonic oscillation of their heading direction relative to the wind, with a frequency mostly in the range 1-17 mHz, corresponding to cycle periods of 1-16 min. The swifts also sometimes performed circling flights at low wind speeds. Wind speed ranged from 1.3 to 14.8 m s(-1), and we expected to find different patterns of orientation at different wind speeds, assuming that the swifts adapt their orientation to avoid substantial displacement during their nocturnal flights. However, oscillatory orientation was found at all wind speeds with variable frequencies/periods that did not show any consistent relationship with wind speed. It remains to be shown whether cyclic heading changes are a regular feature of bird orientation. (+info)
Instrumental methods for studies of structure and function of root systems of large trees.
New methods using different physical principles have been successfully applied in studies of root systems of large trees. The ground-penetrating radar technique provides 3D images of coarse roots (starting with a diameter of about 20 mm) from the soil surface down to a depth of several metres. This can even be done under layers of undisturbed materials such as concrete, asphalt and water. Fine roots cannot be visualized by this method, but the total rooted volume of soil can be determined. The differential electric conductance method has been used for fast measurement of conducting (absorbing) root surfaces. However, more testing is needed. Both these methods are non-invasive. The results can be verified by an almost harmless excavation of whole root systems, including fine roots, using the ultrasonic air-stream (air-spade) method. This method is suitable for all studies, as well as practical operations on roots or objects in their vicinity, where a gentle approach is required. Sap flow measurements on their own or in tandem with soil moisture monitoring play a leading role in studying root function and hydraulic redistribution of flow in the soil. The water absorption function of roots can be studied by measuring sap flow on individual root branches directly (as on crown branches) and also indirectly, by measuring the radial pattern of sap flow in different sapwood depths at the base of a stem. Root zone architecture can also be estimated indirectly by studying its functionality. The heat field deformation method with multi-point sensors has been found to be very convenient for this purpose. A combination of several such methods is recommended whenever possible, in order to obtain detailed information about the root systems of trees. (+info)
Radar evidence for liquid surfaces on Titan.
Arecibo radar observations of Titan at 13-centimeter wavelength indicate that most of the echo power is in a diffusely scattered component but that a small specular component is present for about 75% of the subearth locations observed. These specular echoes have properties consistent with those expected for areas of liquid hydrocarbons. Knowledge of the areal extent and depth of any deposits of liquid hydrocarbons could strongly constrain the history of Titan's atmosphere and surface. (+info)
Tracking butterfly flight paths across the landscape with harmonic radar.
For the first time, the flight paths of five butterfly species were successfully tracked using harmonic radar within an agricultural landscape. Until now, butterfly mobility has been predominantly studied using visual observations and mark-recapture experiments. Attachment of a light-weight radar transponder to the butterfly's thorax did not significantly affect behaviour or mobility. Tracks were analysed for straightness, duration, displacement, ground speed, foraging and the influence of linear landscape features on flight direction. Two main styles of track were identified: (A) fast linear flight and (B) slower nonlinear flights involving a period of foraging and/or looped sections of flight. These loops potentially perform an orientation function, and were often associated with areas of forage. In the absence of forage, linear features did not provide a guiding effect on flight direction, and only dense treelines were perceived as barriers. The results provide tentative support for non-random dispersal and a perceptual range of 100-200 m for these species. This study has demonstrated a methodology of significant value for future investigation of butterfly mobility and dispersal. (+info)
Cassini radar views the surface of Titan.
The Cassini Titan Radar Mapper imaged about 1% of Titan's surface at a resolution of approximately 0.5 kilometer, and larger areas of the globe in lower resolution modes. The images reveal a complex surface, with areas of low relief and a variety of geologic features suggestive of dome-like volcanic constructs, flows, and sinuous channels. The surface appears to be young, with few impact craters. Scattering and dielectric properties are consistent with porous ice or organics. Dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons. (+info)
The sand seas of Titan: Cassini RADAR observations of longitudinal dunes.
The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps. (+info)
Energetic influence on gull flight strategy selection.
During non-migratory flight, gulls (Larids) use a wide variety of flight strategies. We investigate the extent to which the energy balance of a bird explains flight strategy selection. We develop a model based on optimal foraging and aerodynamic theories, to calculate the ground speeds and airspeeds at which a gull is expected to flap or soar during foraging flight. The model results are compared with observed flight speeds, directions, and flight strategies of two species of gulls, the black-headed gull Larus ridibundus and the lesser black-backed gull Larus fuscus. The observations were made using a tracking radar over land in The Netherlands. The model suggests that, especially at combinations of low ground speed (approximately 5-10 m s(-1)), high air speed (approximately 20-25 m s(-1)) and low ground and air speed, gulls should favor soaring flight. At intermediate ground and air speeds the predicted net energy gain is similar for soaring and flapping. Hence the ratio of flapping to soaring may be higher than for other air and ground speed combinations. This range of speeds is broadest for black-headed gulls. The model results are supported by the observations. For example, flapping is more prevalent at speeds where the predicted net energy gain is similar for both strategies. Interestingly, combinations of air speed and flight speed that, according to the model, would result in a loss of net energy gain, were not observed. Additional factors that may influence flight strategy selection are also briefly discussed. (+info)