me AMOS iu-70 Automatic Paul L. Hexter and Richard H. Waters

ESSA-Weather Bureau

Meteorological Observing station

Silver Spring, Md.

1. Introduction

Weather Bureau use of automatic surface weather ob-serving equipment began in 1945 with the installation of three wind and pressure reporting stations in south-ern Florida. Data from these stations were used to aid in the forecasting of hurricane movement and intensity. In 1953, the first Automatic Meteorological Observing Station (AMOS-I) equipment was developed by the Weather Bureau. The characteristics of the AMOS-I and improved versions, AMOS II and III , are given in Table 1 (Hill, 1967). Twenty-one AMOS III stations were installed in the field and 18 are still operational. However, the AMOS Ill 's have approached, if not passed, their useful lifetime and replacement stations are now required due to the lack of spare parts.

Automatic weather stations may vary in complexity from a simple data logger which merely records raw data, through an intermediate station which performs limited processing and transmits the data, to a complex station which has a built-in computer to perform calcu-lations such as the reduction of pressure to sea level. In 1965, the Weather Bureau decided to support the development of the "intermediate" or AMOS I I I type of automatic weather station. Individuals representing the operational arm of the Weather Bureau, on the one hand, and the research and development arm, on the other, collaborated in developing specifications for an updated, state-of-the-art, version of the AMOS I I I known as the AMOS 111-70.*

* It is anticipated that the first of these stations will be in-stalled in the field in 1970.

2. Concept of use

The concept of use of the AMOS 111-70 is based on the premise that a device is needed to supplement, not re-place, human observations. There are so many subjective aspects of the surface weather observation that complete automation will likely be more than 10 years in the fu-ture, and will require a new set of observational rules, definitions and criteria. The AMOS III—70 is designed to perform a few of the repetitive duties of the observer, such as reading the hygrothermometer, barometer, wind instruments and raingage and reporting the data on tele-type. Another primary use of the AMOS 111-70 is to fill in for the observer at part-time observing stations so that at least some of the basic meteorological measure-ments enter the weather system when the observer is not on duty.

There are four major types of observational networks which can use the AMOS III—70: aviation, urban, marine and sub-synoptic. For aviation, the AMOS III—70 could be used primarily at small airports, particularly those that are manned part-time. The urban use includes air pollution and local forecasting; "spider" networks of these stations could transmit via dedicated teletype to a metropolitan forecast office. The "marine" category includes stations on lakes and inland waterways as well as coastal points; of particular interest are Coast Guard facilities which have provided surface observations but which are being fully automated. The sub-synoptic cate-gory includes stations needed to provide mesoscale ob-servations and any additional "basic" observational sites not located at airports.

TABLE 1.

Designation Approximate

date of development

Parameters reported Modular design Power Method of

transmission Remarks

AMOS-I 1953 Temperature No A.C. Teletypewriter Electro-mechanical; below normal speed trans-Humidity- mission Pressure Wind speed Wind direction Precipitation

AMOS-II 1954 (Same as for AMOS-I) No A.C. Teletypewriter Electro-mechanical; full-speed transmission and AMOS-II (Same as for AMOS-I) conventional format

AMOS-III 1959 As above with modu- Yes A.C. Teletypewriter Electro-mechanical; provision for adding remarks AMOS-III lar add-on capability at end of message; analog data display capability.

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3. Data reported

The parameters to be reported by the AMOS III—70 for each major use are given in Table 2. The seven parame-ters above the solid line are the primary parameters mea-sured by the basic station. Those below the line are add-on parameters, which are planned for later develop-ment. The actual parameters reported from each station will vary with specific location requirements and availa-bility of sensors. A manual input device and remarks module will be available at aviation stations; these ad-juncts will enable the observer to enter manually cloud layers and ceiling, visibility, obstructions to visibility and pertinent remarks.

The parameter specifications for the primary parame-ters are given in Table 3. These specifications were ar-rived at through the joint efforts of the "operational" and "development" arms of the Weather Bureau staff. In arriving at these specifications, operational needs were considered along with the constraints of engineering realities, operation in the field environment, and cost.

4. Description of the station

In its present configuration the AMOS III—70 Auto-matic Meteorological Observing Station weighs 50 pounds; fits into a standard rack drawer 19 inches deep, 19 inches wide and 9 inches high and can accept data from seven meteorological sensors. They are tempera-ture, dew point, wind direction, wind speed, altimeter setting, precipitation accumulation and precipitation oc-currence (is it raining now, or has it rained during the past hour?). See Figs. 1-3. In addition, the station has the capability of immediate expansion. As many as six additional parameter processing modules can be accom-modated. The output of the station feeds directly into a Baudot encoded teletype circuit. A hardcopy output

TABLE 3. Parameter specifications.

Parameter Sensor type Range System resolution

Performance accuracy Reporting mode

Ambient air temperature Hygrothermometer — 60F to +120F 1 ° F ± 1 ° F Degrees Fahrenheit or

— 80F to+lOOF Dew point temperature Hygrothermometer — 30F to +90F 1°F ±1°F* Degrees Fahrenheit Altimeter setting Aneroid Minimum range 0.01" Hg ± .03" Code (e.g., 992 = 29.92" Altimeter setting

of 3" over Hg.) spread of 27.0" to 31.5" Hg

Wind direction Viscous damped vane 0° to 360° 10° ± 5 ° Tens of degrees Wind speed Pulse count anemometer** 0 to 125 knots 1 knot ± 2 knots or Knots Wind speed

3% whichever is greater

Cumulative precipitation Tipping bucket*** 0 to 9.99" 0.01" ±0.02" or 10% Code to nearest hundredth Cumulative precipitation Tipping bucket*** of reading of inch

Current precipitation Rotating disk type or selective Yes/No Yes/No Yes/No indication precipitation indicator

* ± 1 F above 40F, ± 5 F at -30F . ** 1 minute average.

*** Cumulative since last 6 hour reading.

is thereby available from a teletypewriter or tape punch. See Fig. 4.

Functional description. Station inputs are derived from sensors in common use by the Weather Bureau. Sensor output data in the form of pulse duration, pulse count or yes-no signals are converted within the station to a binary-coded decimal (BCD) representation of the value of the parameter in appropriate engineering units. Following such initial processing, the value of each is stored in an output register "ready" for interrogation. Upon receipt of the station call over a teletype line, transmission of the message is initiated. The "message composer" calls-up the output register of each parameter processing module serially by digit. After code conver-sion to Baudot, each digit of the message is formatted for direct insertion serially by bit, into the teletype

TABLE 2. Data reported.

Parameter Use

Aviation Urban Marine Sub-synoptic

Pressure (altimeter set- X X X ting)

Temperature X X X X Humidity (dew point X X X

temperature) Wind speed X X X X Wind direction X X X X Cumulative precipitation X X X Precipitation occurrence X X X

Visibility X X Cloud height X Tide level X Wave height X Water temperature X

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FIG. 1. AMOS III—70, shown in rack drawer, with associated sensors. There are a total of 9 etched circuit boards, 1 for each sensor plus a teletype module and a timing module.

FIG. 2. AMOS 111-70, in standard instrument rack, shown in open position for servicing. Drawer below open drawer contains altimeter setting digitizer. Space above drawers and below teletype is empty.

FIG. 3. AMOS 111-70, as in Fig. 2, but with AMOS 111-70 drawer in normal, closed position.

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FIG. 4. Teletype printout from AMOS III—70. Observations are at 1-min intervals. First observation reads: temperature 58F, dew point 51F, wind direction 110°, wind speed 7 knots, altimeter setting 29.97 inches, precipitation is occurring. "PH" indicates that precipitation has occurred during the past hour, but is not occurring at the time of observation. The figures "036" in the tenth observation indicates that .36" of rain has occurred during the past 6 hours.

All data shown are automatically reported. Manual data, such as clouds, weather and prevailing visibility, may be added with manual input device (not shown). Location and date/time group are also not shown in this sample, which was made in the laboratory. This information would appear in the Service A teletype message.

circuit. T o prevent transmission of erroneous data as the result of an output register changing during call-up, an inhibit signal prevents the placement of a new value in the parameter register while that parameter is being transmitted. Housekeeping characters, such as slants between temperature and dewpoint, which are required in the message format, are automatically inserted through the message composer. Following transmission of all pa-rameter data an "end of message" signal stops transmis-sion and holds the system in a "ready" state for the next interrogation.

Design philosophy. Station reliability, packaging and maintainability were of prime concern in the design of the AMOS III—70. In the past, equipments of the inter-mediate type, built of discrete components, exhibited a mean time between failure (MTBF) on the order of 500 hours. Estimates indicated that through the application of modern components and techniques, especially inte-grated circuits, an M T B F of 5000 hours could be ex-pected. From the standpoint of equipment packaging, discrete components have been assembled as circuit or logic modules in the past. The employment of integrated circuits allows assembly of function modules, providing

compactness and a high degree of miniaturization. Equip-ment maintenance has been simplified through a pack-aging concept which results in a system that is modular on a weather parameter basis rather than on the basis of logic function. That is, if temperature fails in a sys-tem modular by logic functions, one must trouble-shoot the associated components. Whereas, if the system is modular by weather parameter, it is necessary to replace the temperature module only.

5. Future plans

Tests of two prototype models have begun at the Weather Bureau's Test and Evaluation Laboratory. The engineering test program will determine how well the system meets design specifications in the areas of con-struction, reliability, maintainability, and operational use. In addition, there will be a functional test designed to determine how closely the measurement transmitted by the AMOS III—70 approximates similar measurements transmitted by a human observer.

The operational systems will be built by industry and will be identical copies of the Weather Bureau prototype. Cost of the basic system including sensors but exclusive of installation costs is estimated at $10,000. Initially, it is planned to install the AMOS III—70 equipment at air-ports in Alaska where observers are on duty only part-time, and at other locations to replace the obsolete AMOS-III system. Later installations will be made at urban and marine locations in addition to airports.

Additional modules soon to be developed provide manual input and remarks capability, visual display, and runway visibility. Later developments will include the measurement of wind gusts, cloud height, wave height, tide level, water temperature, and capability to transmit over radio rather than teletype.

It is also planned to develop a "remote" AMOS to be battery powered, for use in isolated locations, and a substation data logger, to record max-min temperature and precipitation for climatological records. The even-tual development of a "sophisticated" AMOS, for use at major airports, would complete the family of auto-matic stations. These stations can only be successfully developed through the cooperative efforts of operations and development groups; through these efforts, it is hoped that the observer of the future will be able to take advantage of the rapidly advancing technology of automation.

Reference Hill, A. N., 1967: Automatic weather stations in the U. S.

Weather Bureau—past, present and immediate future. World Meteorological Organization, Technical Note No. 82, Automatic Weather Stations, WMO-No. 200, TP. 104, 19-93.

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