A new visibility instrument, the forward scatter visibility meter, has been developed. This report describes the development of the instrument, including the various field tests. Some thirty instruments have been operationally deployed in a network of automatic weather stations near L.G. Hanscom Field in Bedford, Mass. Comparisons between field instruments and transmissometers yield differences of about plus or minus 19 percent. Comparisons with visual observations show differences of plus or minus 34 percent and greater. Analyses of individual cases uncovered difficulties with the response time of observers and with ability to diagnose spatially varying visibility. The accuracy of visibility measurements is assessed and the report concludes by looking at the future of visibility instruments. (Author).

An examination of objective forecast techniques using sensor equivalent visibility to forecast fine scale variations in visibility was conducted with approximately two yr of radiation fog data collected in the AFCRL mesonet-work. Using stepwise screening regression and Regression Estimation of Event Probability (REEP) techniques, the results demonstrated the usefulness of a network of remote sensors around an airfield in objectively predicting short time scale fluctuations of airfield runway visibility. The REEP technique in particular generated exceedance probabilities that display positive skill relative to a conditional climatology model (Markov) of proven validity. Skill by subjective forecasters was also demonstrated using the REEP output as guidance in the generation of short-range forecasts out to one hr. The necessity for additional network stations away from the runway was demonstrated since statistical techniques utilizing runway visibility observations only, when applied to independent data, showed large negative skill relative to the Markov model in contrast to positive skill achieved using 8 network stations of varying distances out to 16 km from the runway.

The determination of subjective weather observations through the use of an automated array of weather sensors coupled with a decision tree program was examined through analysis of data gathered at the AFGL Weather Test Facility at Otis AFB, Mass. This report describes the instruments used in the array, the response of the instruments to type of weather observed, and the decision tree programs. Preliminary results indicate that a computer-controlled weather sensor array has potential value in determining objectively those types of weather previously relegated to human responsibility.

One of the primary objectives of this program was to design a developmental model ALWOS for the lowest possible cost. Reliability and maintenance costs over the life of the system were considered in addition to the initial purchase and installation costs. To this end, field proven, off the shelf components were used wherever possible throughout the system. Another primary objective was modularity of design. The hardware and software were constructed to allow flexibility in interfacing a variety of sensors or adding additional sensors to measure new parameters. The ALWOS as configured at Dulles Airport is a low-cost and flexible system which can provide an automatic weather observation from the data acquisition, processing and display point of view, with the potential for good long-term system reliability. After a period of familiarization with the equipment and dealing with an assortment of system and sensor problems, the functioning of the system became relatively trouble-free. Evaluation of the ALWOS supports the generally accepted concept that automated, low-cost weather observation systems can indeed perform such a function given suitable sensing devices. (Author).

The potential for remote tower measurements of point visibility in the determination of slant range visibility for aircraft landing operations was explored through analysis of data collected at the Air Force Geophysics Laboratory Weather Test Facility at Otis AFB, Massachusetts. This report described initial experiments that deal with an analysis of the small scale variability of extinction coefficient in time and space. Data from two instrumented towers spaced 1500 ft apart were classified for investigation of the horizontal variability of visibility at elevations up to 100 ft and space-time variability for lag periods from 0 to 10 minutes. The preliminary tests give additional evidence that the runway visual range (RVR) measurements alone often are not representative of pilot visibility during approach and touchdown. Remote measurements of visibility using either a 50-ft or 100-ft instrumented tower would add significantly to the real safety of 'see-to-land' operations under conditions of Categories I, II, and IIIa through an improved description of conditions related to airfield visibility. (Author).