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A Revolution in Remote Sensing Is Under Way
Click to have a closer look. Select version. About this book Contents Customer reviews Related titles. Images Additional images. Contents 1. Customer Reviews Review this book. Current promotions. We find that bending angle error is roughly similar for all current GPS transmitters about 0.
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An investigation of the transmitter clock spectra reveals this is due to more power in periods between sec. We conclude by summarizing the tested GNSS clock estimation and application strategies in the context of current and future radio occultation missions. In the GPS radio occultation technique , the atmospheric excess phase AEP can be used to derive the refractivity, which is an important quantity in numerical weather prediction.
These two techniques , however, rely on the reference data in the data processing, increasing the complexity of computation.
A variational regularization of Abel transform for GPS radio occultation. While concise and straightforward to apply, the AI accumulates and propagates the measurement error downward. The measurement error propagation is detrimental to the refractivity in lower altitudes. In particular, it builds up negative refractivity bias in the tropical lower troposphere.
An alternative to AI is the numerical inversion of the forward Abel transform, which does not incur the integration of error-possessing measurement and thus precludes the error propagation. The variational regularization VR proposed in this study approximates the inversion of the forward Abel transform by an optimization problem in which the regularized solution describes the measurement as closely as possible within the measurement's considered accuracy.
The optimization problem is then solved iteratively by means of the adjoint technique. VR is formulated with error covariance matrices, which permit a rigorous incorporation of prior information on measurement error characteristics and the solution's desired behavior into the regularization. VR holds the control variable in the measurement space to take advantage of the posterior height determination and to negate the measurement error due to the mismodeling of the refractional radius. The advantages of having the solution and the measurement in the same space are elaborated using a purposely corrupted synthetic sounding with a known true solution.
The comparison to nearby radiosonde observations shows that VR attains considerably smaller random and systematic errors compared to AI.
A noteworthy finding is that in the heights and areas that the measurement bias is supposedly small, VR follows AI very closely in the mean refractivity. Hinson, David P. Leonard; Weaver, Harold A. The observation was performed with signals transmitted simultaneously by four antennas of the NASA Deep Space Network, two at the Goldstone complex in California and two at the Canberra complex in Australia. Each antenna radiated 20 kW without modulation at a wavelength of 4.
New Horizons received the four signals with its 2.
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Each REX relied on a different ultra-stable oscillator as its frequency reference. The signals were digitized and filtered, and the data samples were stored on the spacecraft for later transmission to Earth. Six months elapsed before all data had arrived on the ground, and the results reported here are the first to utilize the complete set of observations. Pluto's tenuous atmosphere is a significant challenge for radio occultation sounding, which led us to develop a specialized method of analysis.
We began by calibrating each signal to remove effects not associated with Pluto's atmosphere, including the diffraction pattern from Pluto's surface. We reduced the noise and increased our sensitivity to the atmosphere by averaging the results from the four signals, while using other combinations of the signals to characterize the noise. We then retrieved profiles of number density, pressure, and temperature from the averaged phase profiles at both occultation entry and exit.
Finally, we used a combination of analytical methods and Monte Carlo simulations to determine the accuracy of the measurements. The REX profiles provide the first direct measure of the surface pressure and temperature structure in Pluto's lower atmosphere. There are significant differences between the structure at entry Recent analysis of changes in the hydrological sensitivity during a recent weakening of transient warming show that the representation of the processes linking the condensation of water vapor and the growth and invigoration of convective precipitation produce the greatest disparities between cloud resolving models and current observations of convective cloud systems.
The temperature and moisture structure of a cloud environment is the main control on the thermodynamical processes leading to the development of precipitation.
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The surrounding environmental state acts as the broader sink and source for moisture exchange between clouds and their surroundings. As precipitation develops, water vapor condensation leads to an evolving 3D temperature and moisture structure in and near clouds different from the larger scale structure or the clear-sky environment. Yet there is a gap in existing space-based observations since conventional IR and microwave sounding data are degraded in the presence of clouds and precipitation.
GNSS radio occultations RO are a low-cost approach to sounding the global atmosphere with high precision, accuracy and vertical resolution inside clouds and across land-ocean boundaries. GNSS provides reliable, sustained signal sources. While current RO provide no direct information on the associated precipitation state, a recently studied concept of Polarimetric RO PRO can characterize the moist thermodynamics within precipitating systems.
Since precipitation-sized hydrometeors are non-spherically shaped, precipitation induces a cross-polarized component during propagation through clouds, recorded by a dual-channel RO receiver as a differential phase shift. The ionosphere of Europa from Galileo radio occultations. The Galileo spacecraft performed six radio occultation observations of Jupiter's Galilean satellite Europa during its tour of the jovian system. Such an ionosphere could be produced by solar photoionization and jovian magnetospheric particle impact in an atmosphere having a surface density of about 10 8 electrons per cubic centimeter.
In either case, these temperatures are much higher than those observed on Europa's surface, and an external heating source from the jovian magnetosphere is required. Temperatures retrieved from Mars Global Surveyor radio occultations have been searched for evidence of waves. The profiles exhibit an undulatory behavior that is suggestive of vertically propagating waves. The undulatory structure is most pronounced between latitudes 29 deg N and 10 deg S, usually in regions of "interesting" topography, e.
Several temperature profiles, particularly within 30 deg of the equator, exhibit lapse rates that locally become superadiabatic near the 0. This implies that the waves are "breaking" and depositing horizontal momentum into the atmosphere.
Such a deposition may play an important role in modulating the atmospheric winds, and characterizing the spatial and temporal distribution of these momentum transfers can provide important clues to understanding how the global circulation is maintained. Vogt, Marissa F. Radio occultation electron densities measurements from the Mariner 9 and Viking spacecraft, which orbited Mars in the s, have recently become available in a digital format.
These data are highly complementary to the radio occultation electron density profiles from Mars Global Surveyor, which were restricted in solar zenith angle and altitude. We find that the electron densities measured by radio occultation are in generally good agreement with the MARSIS data and model, especially near the altitude of the peak electron density but that the MARSIS data and model display a larger plasma scale height than the radio occultation profiles at altitudes between the peak density and km. Consequently, the MARSIS-measured and model electron densities are consistently larger than radio occultation densities at altitudes km.
Finally, we have analyzed transitions in the topside ionosphere, at the boundary between the photochemically controlled and transport-controlled regions, and identified the average transition altitude, or altitude at which a change in scale height occurs. The average transition altitude is km in the Mariner 9 and Viking radio occultation profiles and in profiles of the median MARSIS radar sounding electron densities. Cassini orbits around Saturn were designed to provide eight optimized radio occultation observations of Saturn's rings during summer, Three monochromatic radio signals 0.
A rich data set has been collected.