The relation between the shock-induced free-surface velocity and the postshock specific volume of solids

The release of solids from a state of shock compression at a free surface is examined. For isentropic release, the postshock specific volume V[prime]0 is shown to be constrained by V[prime]0? (Ufs–Up)2/P1+V1, where (P1,V1) is the pressure-volume Hugoniot state of shock compression and Ufs and Up are the free-surface and shock particle velocities, respectively. When a sudden phase change occurs during the release process, this lower bound is increased, subject to simplifying assumptions about the phase transition

Development of Great Lakes algorithms for the Nimbus-G coastal zone color scanner

A series of experiments in the Great Lakes designed to evaluate the application of the Nimbus G satellite Coastal Zone Color Scanner (CZCS) were conducted. Absorption and scattering measurement data were reduced to obtain a preliminary optical model for the Great Lakes. Available optical models were used in turn to calculate subsurface reflectances for expected concentrations of chlorophyll-a pigment and suspended minerals. Multiple nonlinear regression techniques were used to derive CZCS water quality prediction equations from Great Lakes simulation data. An existing atmospheric model was combined with a water model to provide the necessary simulation data for evaluation of the preliminary CZCS algorithms. A CZCS scanner model was developed which accounts for image distorting scanner and satellite motions. This model was used in turn to generate mapping polynomials that define the transformation from the original image to one configured in a polyconic projection. Four computer programs (FORTRAN IV) for image transformation are presented

Multiwavelength optical pyrometer for shock compression experiments

A system for measurement of the spectral radiance of materials shocked to high pressures (~100 GPa) by impact using a light gas gun is described. Thermal radiation from the sample is sampled at six wavelength bands in the visible spectrum, and each signal is separately detected by solid-state photodiodes, and recorded with a time resolution of ~10 ns. Interpretation of the records in terms of temperature of transparent sample materials is discussed. Results of a series of exploratory experiments with metals are also given. Shock temperatures in the range 4000–8000 K have been reliably measured. Spectral radiance and temperatures have been determined with uncertainties of 2%

Shock temperature measurements in Mg_2SiO_4 and SiO_2 at high pressures

Temperatures in the high pressure shock state have been determined by measurement of optical radiation from pure samples of forsterite (Mg_2SiO_4), α-quartz, and fused silica. Shock waves of known amplitude were produced by tantalum flyer impact using a two-stage light gas gun. Shock pressures in the ranges 150-175 GPa and 70-115 GPa for Mg_2SiO_4 and SiO_2 respectively were achieved, and temperatures in the range 4500-6800 K were measured. The observed temperatures in Mg_2SiO_4 are consistent with the occurrence of a shock-induced phase transition with a transition energy of ∼ 1.5 MJ/kg. Measured Hugoniot temperatures versus pressure in both fused and crystalline SiO_2 shocked to the stishovite regime suggest the occurrence of a previously unknown transition, beginning at pressures of approximately 107 GPa and 70 GPa for α-quartz and fused quartz, respectively. The energies and temperatures appear to be consistent with the onset of melting of stishovite under shock loading

Evaluation of ERIM optically processed SEASAT SAR data

The results of three studies on the radiometric and geometric properties of optically processed SEASAT SAR imagery are summarized. The accuracy with which the image scale can be predicted based upon a knowledge of the SAR platform and recording system parameters and the processor characteristics was evaluated. The considerations involved in making radiometric measurements from image films, the use of point targets for calibrating the effects of Doppler spectrum shifts on the radiometric calibration of the SAR image data over extended swath lengths was evaluate

One-dimensional isentropic compression

The generation of nearly isentropic pressure‐density states in a molecular fluid sample, e.g. H_2O is examined by a series of one‐dimensional finite difference calculations. We employ a series of buffer materials of increasing shock impedance (Lexan, Al, Fe, W) behind the sample and impact it with a composite flyer plate of the same series of materials. In the case of H_2O impacted at 2.5 km/sec, three‐fold nearly isentropic compression to a pressure of 70 GPa is achieved in 10 μsec with a 3 cm thick composite impactor

Verification of reflectance models in turbid waters

Inherent optical parameters of very turbid waters were used to evaluate existing water reflectance models. Measured upwelling radiance spectra and Monte Carlo simulations of the radiative transfer equations were compared with results from models based upon two flow, quasi-single scattering, augmented isotropic scattering, and power series approximation. Each model was evaluated for three separate components of upwelling radiance: (1) direct sunlight; (2) diffuse skylight; and (3) internally reflected light. Limitations of existing water reflectance models as applied to turbid waters and possible applications to the extraction of water constituent information are discussed

Shock temperatures of SiO_2 and their geophysical implications

The temperature of SiO_2 in high-pressure shock states has been measured for samples of single-crystal α-quartz and fused quartz. Pressures between 60 and 140 GPa have been studied using projectile impact and optical pyrometry techniques at Lawrence Livermore National Laboratory. Both data sets indicate the occurrence of a shock-induced phase transformation at ∼70 and ∼50 GPa along the α- and fused quartz Hugoniots, respectively. The suggested identification of this transformation is the melting of shock-synthesized stishovite, with the onset of melting delayed by metastable superheating of the crystalline phase. Some evidence for this transition in conventional shock wave equation of state data is given, and when these data are combined with the shock temperature data, it is possible to construct the stishovite-liquid phase boundaries. The melting temperature of stishovite near 70 GPa pressure is found to be 4500 K, and melting in this vicinity is accompanied by a relative volume change and latent heat of fusion of ∼2.7% and ∼2.4 MJ/kg, respectively. The solid stishovite Hugoniot centered on α-quartz is well described by the linear shock velocity-particle velocity relation, u_s = 1.822 up + 1.370 km/s, while at pressures above the melting transition, the Hugoniot centered on α-quartz has been fit with u_s = 1.619 u_p + 2.049 km/s up to a pressure of ∼200 GPa. The melting temperature of stishovite near 100 GPa suggests an approximate limit of 3500 K for the melting temperature of SiO_2-bearing solid mantle mineral assemblages, all of which are believed to contain Si^(4+) in octahedral coordination with O^(2−). Thus 3500 K is proposed as an approximate upper limit to the melting point and the actual temperature in the earth's mantle. Moreover, the increase of the melting point of stishovite with pressure at 70 GPa is inferred to be ∼11 K/GPa. Using various adiabatic temperature gradients in the earth's mantle and assuming creep is diffusion controlled in the lower mantle, the current results could preclude an increase of viscosity by more than a factor of 10^3 with depth across the mantle

The temperature of shock-compressed water

Temperatures from 3300–5200 K were measured in liquid H2O shocked to 50–80 GPa (500–800 kbar). A six-channel, time-resolved optical pyrometer was used to perform the measurements. Good agreement with the data is obtained by calculating the temperature with a volume-dependent Grüneisen parameter derived from double-shock data and a heat capacity at constant volume of 8.7 R per mol of H2O