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Measuring seismic properties of fine sediments in an off-Earth environment
Published in Ömer Aydan, Takashi Ito, Takafumi Seiki, Katsumi Kamemura, Naoki Iwata, 2019 Rock Dynamics Summit, 2019
M.A. Dello-Iacovo, S. Saydam, R.C. Anderson
The pressure is measured in inches of mercury (in.Hg) relative to Earth sea level atmospheric pressure. A reading of 0 in.Hg indicates room pressure. A true reading of -30 in.Hg is analogous to vacuum. A reading of around -29.7 in.Hg is approximate to Mars atmosphere (1 % Earth atmosphere). The chamber and pump are capable of achieving pressures of around -29 in.Hg (~3 % Earth atmosphere), which is sufficient for our measurement purposes.
Measurement fundamentals and instrumentation
Published in Raymond F. Gardner, Introduction to Plant Automation and Controls, 2020
Fluid pressure—usually air—is applied against a liquid in a U-tube as shown in Figure 1.4. The pressure forces the liquid to rise in the U-tube until the liquid weight balances the pressure force. The measurement is the height of the liquid in the manometer. For small pressure measurements, such as fan-discharge pressures, water is often used, and the pressure is given in inches of water column. For larger pressures or vacuum, mercury is used, and the units are given in inches of mercury. Standard atmospheric pressure is slightly less than 30 inches of mercury. To increase the sensitivity, manometers are often inclined at an angle. To convert height of liquid to psip=γ⋅h(whereγisweightdensity)Find: How high in feet of water column is one psi?1lbfin2=62.41bft3⋅ft2144in2⋅hSolving:h=2.31ft
Air, Noise, and Radiation
Published in Gary S. Moore, Kathleen A. Bell, Living with the Earth, 2018
Gary S. Moore, Kathleen A. Bell
Gravity pulls the atmosphere to earth with the densest part of the atmosphere closest to the surface. About 99 percent of the atmospheric mass is below 30 kilometers, 90 percent is below 12 kilometers, and 75 percent of the atmosphere is below 10 kilometers (Figure 10.5). A column of air exerts a pressure on an object at sea level of 43 Kg.cm2. This pressure can be demonstrated by creating a vacuum in a plastic bottle. The external atmospheric pressure will cause the bottle to collapse. Pressure is defined as the force per unit area and is related to the density of the air such that there is both low pressure and low density at higher altitudes. This can be demonstrated by boiling water first at sea level and then at high altitude. The temperature remains steady at 100°C as gases are released from the boiling water. Boiling the water atop a high mountain peak will occur at a lower temperature of perhaps 90°C, since the pressure is lower and gaseous vapors can escape more readily under lower pressure (Figure 10.6). Atmospheric pressure is measured by a barometer and normally expressed in millimeters or inches of mercury. The pressure at sea level is equal to 760 millimeters mercury (Hg), 29.92 inches of mercury, or 1010 millibars. Pressure and atmospheric density in the troposphere is not constant and varies in response to changes in thermal radiation and air movement. Air that is warmed rises in contrast to the cooler air around it. A hot air balloon uses a propane burner to heat the air inside a fabric envelope causing the balloon and its passengers to rise. The energy driving air movement in the atmosphere is sunlight, which strikes the earth at varying angles, warming the air unevenly. Warmer air becomes less dense, expands, and rises, thereby creating a column of air that is lower in pressure. Cooler air is denser, settles, and is characterized by higher pressure. Differences in pressure cause air to move in both horizontal and vertical patterns. Air tends to move from regions of high pressure to low pressure. Therefore, as sun heats a body of air and it rises, a region of low pressure is created into which flows cooler air. The greater the temperature differences, the larger the pressure differences will be, and the more rapid or violent will be the flow of air. If the air flows horizontally, this is known as wind. The direction of the wind is influenced by the rotation of the earth (Coriolis force—Chapter 1), friction, and the differential warming provided by the sun. Such forces cause air to flow into regions of low pressure in a cyclonic motion and then to rise. This cyclonic motion is counterclockwise in the northern hemisphere and clockwise in the southern hemisphere (Figure 10.7). When cool air descends in the northern hemisphere it is radiated outward in a clockwise motion known as an anticyclone (Figure 10.7). The direction is reversed to a counterclockwise motion in the southern hemisphere. These represent very large-scale air movements and play important roles in the dispersion of air pollutants. Low-pressure migrating cyclones usually are associated with inclement weather including precipitation, clouds, and windy conditions. High-pressure systems normally signal cooler dry air with sunny conditions.
A proposed new model for the prediction of latitude-dependent atmospheric pressures at altitude
Published in Science and Technology for the Built Environment, 2021
The ASOS User's Guide (Automated Surface Observing System 1998) specifies an accuracy of ±0.02 inches of mercury for pressure measurement instruments. At an elevation of 4000 m this corresponds to approximately ±0.11% of the measured value at that elevation. As mentioned previously, every weather observation raw dataset analyzed included compromised and missing data. Data gaps ranged from 1 h to several days for some weather observations. The influence of the missing data on data accuracy was determined by using a time-weighted average of the pressure values and comparing this to the average pressure value. A difference near zero indicated that the missing data had no adverse impact on the accuracy. For most datasets this difference was well below ±0.05% when normalized using the average of both values.