Transient response for automatic gain control with multiple intensity thresholds for image-intensified camera
This paper describes the transient response of an automatic gain control (AGC) with multiple thresholds for intensity in an image-intensified camera. Similar examples have flown in intensified-video systems used in satellites. This paper completes the development of a stable AGC with an improved transient response over the system described in a previous work. The improved transient response uses the integrated scene brightness at various intensity thresholds.
Development of a lateral velocity-controlled MEMS vibratory gyroscope and its performance test
The objective of this paper is to present a velocity-controlled vibratory MEMS gyroscope that achieves consistent output characteristics in the lateral driving dynamics of the system. Through a systematic automatic gain control loop design process, the driving mode dynamics of the gyroscope is first transformed to take account of the velocity envelope; a reference tracking integral control is then employed. For stabilized loop construction, a mathematical development and stability analysis of the feedback loop is presented, which is followed by numerical simulation using practical sensor parameters. The mechanical structure was fabricated using the conventional deep reactive ion etching process and the anodic wafer bonding method. Vacuum-packaged devices were used for the resonant gyroscope operation. An essential fabrication process for realizing the electrical connection through a thick glass substrate was possible by applying a sandblasting process and spin coating process of conductive epoxy. Finally, loop simulation and experimental results verified that the amplitude-controlled property in the driving loop is preserved under the system parameter variation which resulted in enhanced gyroscope output performance in comparison with other driving schemes.
Satellite remote sensing of thermospheric O/N2 and Solar EUV: 2. Data analysis
The companion paper by Strickland et al. (this issue) describes a technique for deriving QEUV and O/N2 from disk observations of OI 135.6-nm and N2 LBH dayglow emission. QEUV refers to the integrated solar EUV energy flux below 45 nm and is derived from knowledge of the 135.6/LBH ratio or O/N2 in conjunction with either the 135.6 nm or LBH intensity. O/N2 refers to the ratio of the atomic oxygen (O) column density to the molecular nitrogen (N2) column density at a given value of the N2 column density. Strickland et al. show that the least uncertainty in derived values O/N2 occurs in the vicinity of an N2 depth of 1017 cm−2. The O/N2 values presented in this paper are referenced to this depth. While QEUV is obtained from the intensity of either 135.6 nm or LBH, O/N2 is obtained from the intensity ratio designated by 135.6/LBH. The technique has been used to derive O/N2 and QEUV values from nadir-viewing far ultraviolet dayglow data obtained by the auroral and ionospheric remote sensor instrument on board the Polar BEAR satellite. Data are considered from single passes on July 15, 16, and 21, 1987, spanning a latitude range from 25° to 55°N. The 3-hour ap index was between 20 and 30 for the first two passes and only about 5 for the third pass. The 135.6-nm and LBH signals were obtained from spectra recorded at a resolution of 3.6 nm from which a background was subtracted followed by integration over the intervals from 134.5 to 139.0 nm and 155.0 to 170.0 nm. Uncertainties were assigned to the signals and their ratios that took into account statistical uncertainties in the true signal and in the subtracted background signal. Profiles of derived O/N2 with uncertainties reflecting the data uncertainties are shown along with mass spectrometer/incoherent scatter (MSIS) O/N2 profiles over 25°–55°N. More structure is seen in the profiles on July 15 and 16, which are more disturbed days than July 21. In all cases, O/N2 increases from high to low latitudes. MSIS also shows such an increase but is much less structured. The results are shown to agree qualitatively with O/N2 values obtained from a general circulation model. Derived QEUV values are in the range from 1.1 to 1.4 ergs cm−2 s−1 and are in good agreement with values derived from the Hinteregger spectrum for the F10.7 values appropriate to the observations. The results illustrate the potential of the technique for monitoring thermospheric dynamics through latitudinal and temporal variations in O/N2 which are signatures of ascending and descending motion in the thermosphere.