A Method for the Reduction of Out-of-Band Measurement Errors in Multi-band Instruments using Synthetic Source Distributions

A method to reduce multi-band sensor measurement biases due to finite out-of-band response is described. The method takes advantage of the fact that out-of-band measurement errors cancel if the calibration source and the measured source have the same spectral distributions—independent of their spectral distributions or the magnitude of a sensor band’s out-of-band response. Using a known spectral responsivity, a synthetic, arbitrary source spectral distribution can replace a realized spectral distribution in the measurement equation and the signal can be calculated rather than measured. Given the freedom to select any arbitrary distribution for the synthetic source, the efficacy of the approach depends on the fidelity of the replication of the measured spectrum by the synthetic source spectrum. To illustrate the method, an example application is given of top-of-the-atmosphere measurements of water-leaving radiance by multi-band filter radiometers on celestial Earth-viewing sensors.

Narrow-band filter for satellite communication systems

Design narrow-band compact filters, based on high-quality waveguide-dielectric resonators with anisotropic materials is the subject of this paper. Filter represents a segment of a rectangular waveguide rotated around the longitudinal axis of the waveguide 90 degrees and containing one or more dielectric inserts that completely fill the resonator along the narrow wall of the waveguide and partially along the wide one. A distinctive feature of the proposed filter is higher slope steepness of the amplitude-frequency characteristic, and high manufacturability in the centimeter range. The designed narrow-band filter satisfies contradictory requirements: it combines narrow bandwidth (≈ 0.1% of center frequency <em>f</em>₀) with low passband insertion loss (≤ 1 dB).

Propagating characteristics of mesospheric gravity waves observed by an OI 557.7 nm airglow all-sky camera at Mt. Bohyun (36.2°N, 128.9°E)

We analyzed all-sky camera images observed at Mt. Bohyun observatory (36.2°N, 128.9°E) for the period of 2017–2019. The image data were acquired with a narrow band filter centered at 557.7 nm for the OI airglow emission at ~96 km altitude. The total of 150 wave events were identified in the images of 144 clear nights. The interquartile ranges of wavelength, phase speed, and periods of the identified waves are 20.5–35.5 km, 27.4–45.0 m/s and 10.8–13.7 min with the median values of 27.8 km, 36.3 m/s and 11.7 min, respectively. The summer and spring bias of propagation directions of northeast- and northward, respectively, can be interpreted as the effect of filtering by the prevailing winds in the lower atmosphere. In winter the subdominant northwestward waves may be observed due to nullified filtering effect by small northward background wind or secondary waves generated in the upper atmosphere. Intrinsic phase speeds and periods of the waves were also derived by using the wind data simultaneously observed by a nearly co-located meteor radar. The nature of vertical propagation was evaluated in each season. The majority of observed waves are found to be freely propagating, and thus can be attributed to wave sources in the lower atmosphere.