RAWS: The spaceborne radar wind sounder

The concept of the Radar Wind Sounder (RAWS) is discussed. The goals of the RAWS is to estimate the following three qualities: the echo power, to determine rain rate and surface wind velocity; the mean Doppler frequency, to determine the wind velocity in hydrometers; and the spread of the Doppler frequency, to determine the turbulent spread of the wind velocity. Researchers made significant progress during the first year. The feasibility of the concept seems certain. Studies indicate that a reasonably sized system can measure in the presence of ice clouds and dense water clouds. No sensitivity problems exist in rainy environments. More research is needed on the application of the radar to the measurement of rain rates and winds at the sea surface

The Case against a Tennessee Income Tax

On November 2 the Tennessee legislature will convene a special session to debate reform of the state tax system. The center of the controversy is whether Tennessee should adopt a personal income tax, as proposed by Gov. Don Sundquist, to close an estimated $400 million budget shortfall. This study finds that a personal income tax in Tennessee would likely have two negative economic effects. First, an income tax would almost certainly reduce economic growth and job creation in the state. The absence of an income tax in Tennessee gives Tennessee a large competitive advantage over other states with which it competes for jobs and businesses. We find, for example, that Kentucky, a state very similar to Tennessee except that it has an income tax, has had considerably weaker economic performance since 1980. Between 1980 and 1998 the per capita economic growth rate of Tennessee was 47 percent compared to 36 percent in Kentucky. The second negative effect of a state income tax would be to trigger much faster growth in state expenditures. That has been the almost universal pattern in other states after they enacted a state income tax. Yet the premise of pro-income tax forces in Tennessee that the state's revenues have been growing too slowly is contradicted by the evidence. In the 1990s, even without an income tax, Tennessee's per capita tax receipts have grown 12th fastest among the 50 states. Tennessee's tax revenues have climbed at twice the rate of inflation plus population growth. The legislature should be cutting taxes, not introducing new ones

A satellite-borne radar wind sensor (RAWS)

Modeling global atmospheric circulations and forecasting the weather would improve if worldwide information on winds aloft were available. Accurate prediction of weather is important to agriculture, shipping, air traffic, and many other fields. Global system models of climate are of great importance. Current global atmospheric models use pressure measurements and thermodynamic properties to calculate the effects of wind for use in Numerical Weather Prediction (NWP) models. Inputs to the NWP models are temperature, pressure and wind velocities at different heights. Clearly direct wind measurements could significantly improve the NWP model performance. The RAdar Wind Sounder (RAWS) program at the University of Kansas is a study of the feasibility and the trade-offs in the design of a space-based radar system to measure wind vectors. This can be done by measuring the Doppler shift of cloud and rain returns from three or more points and calculating the components of the wind vector. The RAWS study to date uses the candidate system selected after preliminary study of frequencies and sensitivities. Two frequencies chosen, 10 and 35 GHz, allow higher sensitivity for clouds and more penetration for rain. The past year was devoted to modeling the signal-to-noise ratio (SNR) achievable for the two frequencies. The determination of SNR versus cloud penetration depth used a cloud backscattering and attenuation model in the appropriate radar equation. Calculations assumed reasonable losses in reception and transmission, in addition to the atmospheric attenuation. We discovered that ice clouds provide a higher SNR than previously calculated, but some water clouds give lower SNRs than we calculated before. One of the primary issues in the SNR calculation was the choice of the drop size distribution. Although Xin used several distributions (e.g., log normal, Khrigian and Mazin), this year we used the Deirmendjian cloud model. SNR versus cloud penetration plots were generated to validate the candidate system. Rain, which appears in the cloud models at the lower altitudes, provides ample SNR, as do the higher clouds composed of ice particles. However, in some cloud situations we found the sensitivity for the clouds was marginal or inadequate. At 35 GHz, two of the cloud models characterized by 1 to 2 g/cu m of water content at altitudes extending from 150 to 1500 meters, produced a sufficient SNR. Other models, however, with water contents ranging from 0.5 to 4 g/cu m and altitudes up to 4000 meters, exhibit SNR of -3 to -23 dB, largely because of attenuation in the upper cloud layers. These results coupled with the lower SNR at 10 GHz, led to an investigation of alternate frequencies. The rain present beneath these clouds provides adequate SNR at 10 GHz, and in most cases, at GHz

Fixed versus Flexible: Lessons from EMS Order Flow

This paper addresses the puzzle of regime-dependent volatility in foreign exchange. We extend the literature in two ways. First, our microstructural model provides a qualitatively new explanation for the puzzle. Second, we test implications of our model using Europe's recent shift to rigidly fixed rates (EMS to EMU). In the model, shocks to order flow induce volatility under flexible rates because they have portfolio-balance effects on price, whereas under fixed rates the same shocks do not have portfolio-balance effects. These effects arise in one regime and not the other because the elasticity of speculative demand for foreign exchange is (endogenously) regime-dependent: low elasticity under flexible rates magnifies portfolio-balance effects; under credibly fixed rates, elasticity of speculative demand is infinite, eliminating portfolio-balance effects. New data on FF/DM transactions show that order flow had persistent effects on the exchange rate before EMU parities were announced. After announcement, determination of the FF/DM rate was decoupled from order flow, as predicted by the model.

Investigation of radar backscattering from second-year sea ice

The scattering properties of second-year ice were studied in an experiment at Mould Bay in April 1983. Radar backscattering measurements were made at frequencies of 5.2, 9.6, 13.6, and 16.6 GHz for vertical polarization, horizontal polarization and cross polarizations, with incidence angles ranging from 15 to 70 deg. The results indicate that the second-year ice scattering characteristics were different from first-year ice and also different from multiyear ice. The fading properties of radar signals were studied and compared with experimental data. The influence of snow cover on sea ice can be evaluated by accounting for the increase in the number of independent samples from snow volume with respect to that for bare ice surface. A technique for calculating the snow depth was established by this principle and a reasonable agreement has been observed. It appears that this is a usable way to measure depth in snow or other snow-like media using radar

Property

Covers cases on the hostile intent requirement in adverse possession, on riparian rights in floodwaters and the common enemy doctrine, on the duty to inquire as to easements in the contract to convey free from encumberance (Moore), and on agreements to return goods in the same condition (Quinn)

Precipitation measurement using SIR-C: A feasibility study

A precipitation detection and measurement experiment is planned for the SIR-C/X-SAR mission. This study was conducted to determine under what conditions an off-nadir experiment is feasible. The signal-to-clutter ratio, the signal-to-noise ratio, and the minimum detectable rain rate were investigated. Available models, used in previous studies, were used for the surface clutter and the rain echo. The study also considers the attenuation of the returns at X band. It was concluded that an off-nadir rain-measurement experiment is feasible only for rain rates greater than 10 mm/hr for look angles greater than 60 deg. For the range of look angles 5 less than theta(sub 1) less than 50, the rain rate required is very high for adequate signal-to-clutter ratio, and hence the feasibility of the experiment

Precipitation measurement using SIR-C: A feasibility study. Investigation at nadir

The most significant limitation of the imaging SAR in rain measurements is the ground return coupled to the rain cell. Here we report a study of the possibility of using the X-SAR and the C-band channel of SIR-C for rain measurement. Earlier signal-to-clutter calculations rule out the use of X-SAR at steeper off-vertical angles of incidence (i.e., 20 less than theta less than 50). Only rain rates greater than 30 mm/hr at angles of incidence greater than 60 degrees showed good signal-to-clutter ratio (SCR). This study involved calculations at vertical incidence. There is adequate signal-to-noise ratio (SNR) at vertical incidence, but the presence of high-range side-lobe levels leads to small SCR for measurement over oceans at both X and C bands. For larger rain thickness (greater than two km), the SCR gets better and smaller rain rates (greater than 10 mm/hr) can be measured. However, rain measurements over forests seem to be feasible at nadir even for smaller rain thickness (less than two km). We conclude that X band may be usable over the forest at vertical incidence to measure rain rates greater than five mm/hr even for shallow rain thickness and over ocean for large rain thickness

Estimation of the rain signal in the presence of large surface clutter

The principal limitation for the use of a spaceborne imaging SAR as a rain radar is the surface-clutter problem. Signals may be estimated in the presence of noise by averaging large numbers of independent samples. This method was applied to obtain an estimate of the rain echo by averaging a set of N(sub c) samples of the clutter in a separate measurement and subtracting the clutter estimate from the combined estimate. The number of samples required for successful estimation (within 10-20%) for off-vertical angles of incidence appears to be prohibitively large. However, by appropriately degrading the resolution in both range and azimuth, the required number of samples can be obtained. For vertical incidence, the number of samples required for successful estimation is reasonable. In estimating the clutter it was assumed that the surface echo is the same outside the rain volume as it is within the rain volume. This may be true for the forest echo, but for convective storms over the ocean the surface echo outside the rain volume is very different from that within. It is suggested that the experiment be performed with vertical incidence over forest to overcome this limitation