On-board accurate calibration of dual-channel radiometers usinginternal and external references

This paper presents a method for combining internal noise injection and external reference standard looks to accurately calibrate an airborne dual-channel radiometer. The method allows real-time estimation of the correct values of the radiometer gains and offsets, even for nontemperature-stabilized radiometers and with minimum loss of measurement time spent in external load measurement. Crosstalk and leakage introduced by the noise injection circuitry is also taken into account, thus providing high gain and offset estimation accuracy. The method was implemented on a National Oceanic and Atmospheric Administration airborne instrument, the Polarimetric Scanning Radiometer, which was used to obtain an extensive set of radiometric measurements over oceanic convection during CAMEX3 in August-September 1998     

Strategy-based interactive cluster visualization for information retrieval

In this paper we investigate a general purpose interactive information organization system. The system organizes documents by placing them into 1-, 2-, or 3-dimensional space based on their similarity and a spring-embedding algorithm. We begin by developing a method for estimating the quality of the organization when it is applied to a set of documents returned in response to a query. We show how the relevant documents tend to clump together in space. We proceed by presenting a method for measuring the amount of structure in the organization and explain how this knowledge can be used to refine the system. We also show that increasing the dimensionality of the organization generally improves its quality, albeit only a small amount. We introduce two methods for modifying the organization based on information obtained from the user and show how such feedback improves the organization. All the analysis is done offline without direct user intervention. Received: 21 December 1998 / Revised: 30 May 1999     

The Ground-Based Scanning Radiometer: A Powerful Tool for Study of the Arctic Atmosphere

Measurements of water vapor and clouds in the polar regions are difficult, because conventional instruments show little sensitivity (~1.3 K/mm) to low amounts. On the other hand, millimeter- and submillimeter-wavelength radiometry offers greatly enhanced sensitivity (up to 51.4 K/mm, depending upon frequency). For this reason, the National Oceanic and Atmospheric Administration's Physical Science Division designed a new instrument, the Ground-Based Scanning Radiometer (GSR), for continuous and unattended observations at millimeter and submillimeter wavelengths (50-380 GHz). The GSR was deployed for the first time during the Arctic winter radiometric experiment in March-April 2004. In this paper, we discuss the GSR calibration procedure, which allows for accurate measurements during clear and cloudy skies. Error-budget analysis and comparison with independent measurements show an absolute accuracy on the order of 1-2 K. Examples of multifrequency and multiangle GSR observations are illustrated, representing a valuable new data set for the study of water vapor, clouds, and atmospheric absorption models in the Arctic.     

Interactive Information Retrieval Using Clustering and Spatial Proximity

A web-based search engine responds to a user’s query with a list of documents. This list can be viewed as the engine’s model of the user’s idea of relevance—the engine ‘believes’ that the first document is the most likely to be relevant, the second is slightly less likely, and so on. We extend this idea to an interactive setting where the system accepts the user’s feedback and adjusts its relevance model. We develop three specific models that are integrated as part of a system we call Lighthouse. The models incorporate document clustering and a spring-embedding visualization of inter-document similarity. We show that if a searcher were to use Lighthouse in ways consistent with the model, the expected effectiveness improves—i.e., the relevant documents are found more quickly in comparison to existing methods.     

Air and sea surface temperature measurements using a 60-GHzmicrowave rotating radiometer

Data obtained from a single-channel scanning 5 mm radiometer on a research vessel were used for the study of sea surface temperature and lower-atmospheric temperature; profiles under neutral, weakly stable, and unstable conditions. Comparisons with in situ air and water temperature measurements, dropsonde temperature data, radiosonde data, and VV Ku-band side-looking radar images are presented. The technique based on 5-mm measurements determines the air-skin water (skin depth of 0.3 mm) temperature difference with an accuracy of the order of 0.1 K. Analysis of the experimental data suggests that the air-skin water temperature difference depends weakly on solar heating and wind speed V for 2.5相似文献