NATIONAL BUREAU OF STANDARDS REPORT

9903

DEVELOPMENT, TESTING, AND EVALUATION OF VISUAL LANDING AIDS

Consolidated Progress Report

For the Period

January 1 to March 31, 1968

By

Photometry Section

Optics Metrology Branch

Metrology Division

Institute for Basic Standards

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3,

1901. Today, in addition to serving as the Nation’s central measurement laboratory,

the Bureau is a principal focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. To this end the Bureau conducts research and

provides central national services in three broad program areas and provides central national services in a fourth. These are: (1) basic measurements and standards,

(2) materials measurements and standards, (3) technological measurements and

standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials

Research, the Institute for Applied Technology, and the Center for Radiation Research.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the

United States of a complete and consistent system of physical measurement, coor- dinates that system with the measurement systems of other nations, and furnishes

essential services leading to accurate and uniform physical measurements throughout

the Nation’s scientific community, industry, and commerce. The Institute consists

of an Office of Standard Reference Data and a group of divisions organized by the

following areas of science and engineering

:

Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic Physics—Cryogenics2—Radio Physics2—Radio Engineering2—Astrophysics2—Time

and Frequency.2 THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to methods, standards of measurement, and data needed by industry, commerce,

educational institutions, and government. The Institute also provides advisory and

research services to other government agencies. The Institute consists of an Office of

Standard Reference Materials and a group of divisions organized by the following areas of materials research:

Analytical Chemistry—Polymers—Metallurgy —- Inorganic Materials — Physical

Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides for the creation of appropriate opportunities for the use and application of technology within the Federal Government and within the civilian sector of American industry. The primary functions

of the Institute may be broadly classified as programs relating to technological meas- urements and standards and techniques for the transfer of technology. The Institute

consists of a Clearinghouse for Scientific and Technical Information,3 a Center for

Computer Sciences and Technology, and a group of technical divisions and offices organized by the following fields of technology:

Building Research—Electronic Instrumentation — Technical Analysis — Product

Evaluation—Invention and Innovation— Weights and Measures —Engineering

Standards—Vehicle Systems Research.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement,

and application of radiation to the solution of Bureau mission problems and the

problems of other agencies and institutions. The Center for Radiation Research consists of the following divisions:

Reactor Radiation—Linac Radiation—Applied Radiation—Nuclear Radiation.

1 Headquarters and Laboratories at Gaithersburg:, Maryland, unless otherwise noted ; mailing address Washington, D. C. 20234.

2 Located at Boulder. Colorado 80302.

3 Located at 5285 Port Royal Road, Springfield, Virginia 22151.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

2120411 August 27, 1968 9903

2120414

2120641

2120653

DEVELOPMENT, TESTING, AND EVALUATION OF VISUAL LANDING AIDS

Consolidated Progress Report to Ship Installations Division

and

Meteorological Division

Naval Air Systems Command

Department of the N avy

and to Federal Aviation Administration

For the Period

January 1 to March 31, 1968

By

Photometry Section

Optics Metrology Branch

Metrology Division

Institute for Basic Standards

IMPORTANT NOTICE NATIONAL BUREAU OF S’

for use within the Government, and review. For this reason, tt whole or in part, is not autho Bureau of Standards, Washing!

the Report has been speciticall)

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

iss accounting documents intended

subjected to additional evaluation

! listing of this Report, either in

e Office of the Director, National by the Government agency for which

:opies for its own use. <TM§>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Development, Testing, and Evaluation of Visual Landing Aids

January 1 to March 31, 1968

I. REPORTS ISSUED

Report No. Title

9694 Development, Testing, and Evaluation of Visual

Landing Aids, Consolidated Progress Report for

Period October 1 to December 31, 1967.

212. 11-1/68 Photometric Tests of a Neon Obstruction Light Manu

factured by Nelson Lights.

212. 11-2/68 Photometric Tests of a Neon Obstruction Light.

Memorandum

Report

Transmissometer Indicator Zero Shifts.

Memorandum

Report

li Scattered-Light” Errors in Transmissometer

Measurements.

2

II. VISIBILITY METERS AND THEIR APPLICATION

Shipboard Visibility Meter.

The instrument was operated on the roof of the Administration Building

at NBS for all but the last week and a half of this period. Satisfactory operation continued with a few failures. The flash lamp arc did not extinguish when the

instrument was turned on with outdoor temperatures of about 20°F or less. The

lamp always operated properly at higher temperatures. No satisfactory explanation

of this phenomenon has been found. The lamp manufacturer suggests increasing the

charging resistor to 1.5Q or higher. This will be done when the instrument is re- moved from the roof.

The contacts of the thermostat in the electronics box failed, apparently due

to the high inrush current of the heater lamp. The thermostat was replaced and

a resistor installed to reduce the maximum surge current. The contact resistance

of the signal peak-detector dump relay became excessive, causing the output

record to appear noisy. The relay was replaced.

The instrument was removed from the roof March 20. The lamp-photocell

box is being disassembled so drawings can be made of the mechanical parts. As

soon as this is completed, the operation of the instrument will be checked and prepared for shipment to Areata.

During this period all circuit drawings were completed and a preliminary instruction manual was prepared. Work is now in progress on the final instruction

manual to be in the form of an NBS report.

Fog Detector Field Tests.

Low visibility conditions suitable for evaluating the performance of these

devices was limited during this period, but there were enough conditions to check

performance on several occasions. This period has been useful for evaluating long

term stability and operating performance. Details are covered in the individual

reports given below.

The Edison Fog Detector.

Operation of the Edison forward -scatter fog detector was continued. The

external baffle of the light source was changed to eliminate the diffraction of the

light from water droplets accumulating on the baffle. The new baffle was made from

aluminum sheeting, with the same diameter as the red plastic, except that, at the

bottom edge, a long point was formed to put any droplets which accumulate so far

away that refracted light from the source cannot reach the detector. The sensitivity

3

of this unit has continued to decrease until it is only about one-fifth of that when

the new detecting element was installed. Some of the decreased sensitivity may be

from loss in lamp output. The lamp is flickering from failure to fire regularly.

This lamp will be replaced when a new lamp is obtained. The signal still varies

with changes in transmittance although the sensitivity is greatly reduced.

The Hoffman VMS-508A Fog Detectors.

Both of the Hoffman backscatter fog detectors were returned from the manufacturer after repair. The malfunctions were reported to be a faulty emitting

gallium -arsenide diode in one unit and improper optical alinement in the other.

Both units were calibrated at Areata and installed in the field for testing. For

three weeks both units were operated with the output signal recorded for comparison with the transmittance records. In good visibility one unit, S/N007, had a normal minimum reading of 0. 18 milliampere with the signal varying constantly

over 0. 02 ma. , and for similar conditions the unit, S/N005, read approximately

0. 22 ma. with the signal varying by 0. 04 ma. Initially the output of both units was

approximately 1 ma. for transmittances of 0. 1 over a 250-foot baseline —visibility 300

feet (day) or 800 feet (night). After three weeks unit 005 was changed to operate

as a fog detector, which should operate a relay to energize an alarm system when

the visibility decreases to the selected level. In the beginning 005 appeared to

operate the relay as expected, but after a few weeks the relay was energized in

daytime in very good visibility, although a visibility of three miles or less should

have been required. Within another week the relay was energized continuously

both day and night even though the visibility was very good and the controls were set

to require visibility of one mile or less. Unit 007 showed very little sensitivity to changes

in transmittance. At this point the units were changed to record the output of 005

and to operate 007 as a fog detector. The 005 unit did not indicate any response to

changes in transmittance but 007 did energize the relay when transmittance

indicated about the three-mile visibility which was selected. After another two

weeks 007 kept the alarm relay energized for all conditions unless the one mile

or less visibility range was selected and it was nighttime. At this time neither

of the units could be calibrated. The cover glass on the transmitter of unit 007

broke again within one week after being reinstalled in the field. Testing of these

units has been discontinued.

The AGA Fog Detector.

The AGA backscatter fog detector has operated throughout this period without

requiring specific maintenance. It has no facilities for continuously recording the

output signal, but a relay for the alarm device is energized when the backscattered

light balances the pilot signal, which is adjusted by the grey-scale setting. Only

two grey-scale settings have been used during this period. At first the grey-scale

4

was set to 1. 0, which balanced when transmittance over a 250-foot baseline

was approximately 0. 9, and later the grey-scale was set to 1. 5, which balanced

at approximately 0. 85 transmittance. Over a period of months there has been no

noticeable change in the value of transmittance required to obtain a balance. These

tests will continue.

Videograph Fog Detector.

The Videograph fog detector is a visibility meter which operates on the principle of atmospheric backscatter. The basic unit is manufactured in West Germany

by F. Frungel Impulsphysics Corporation. The unit under test is a Videograph B

with internal interrogator, which was procured as one of a group from Automatic

Power, Inc. , through U. S. Coast Guard. The transmitted light is produced by a xenon flash-lamp, which creates a high-intensity flash of very short duration, with

1. 2 to 1. 5 flashes per second. The scattered light is detected by a vacuum phototube; the sampled volume is from 15 to 100 feet in front of the instrument. The

receiver is designed to accept only the light from the pulses of the flash-lamp, to prevent

being affected by daylight. The output of the receiver is indicated by a meter calibrated for visibility in nautical miles and kilometers. An alarm relay is provided

which can be sleeted to close when visibility lowers to 4, 3, 2, or 1 nautical mile.

The Videograph B is energized by a nominal 12 volts direct current supply. It is

eauipped with an automatic internal interrogator to monitor the performance and

insure that the transmitter and receiver are functioning. The performance is checked by

opening a shutter to admit a sample of light from the flash-lamp to the phototube via

a light guide. When operating satisfactorily this light should produce an indication of

0. 8 kilometer visibility.

This unit was operated in the laboratory to determine its performance characteristics

oefore it was installed in the field. A recording milliammeter was connected in series

with the visibility indicator meter. The unit did not have arrangements for installing a recorder, but a visibility meter setting potentiometer provided adjustment to compensate

for the resistance of the recorder. A sensitivity potentiometer is used to adjust the B+

voltage across the phototube; for this unit a setting of 4. 44 was specified as the correct

setting. The USCG stated that this unit had been checked and that this setting gave a correct reading of 0. 8 kilometer on the performance check. When the checks were

performed at Areata the sensitivity setting had to be reduced to 1. 75 to achieve the

correct reading. The unit operated satisfactorily on a 12-volt battery, but using a limited-current battery charger on the battery caused erratic performance. A power

supply with a well-filtered output gave satisfactory operation. The operation in the

laboratory showed response to atmospheric changes. The unit will be installed in the

field for regular performance operation early next quarter.

5

AGA Visibility Meter.

A visibility meter developed by AGA Aktiebolog was obtained on a 6-month loan for

feasibility evaluation. This equipment is a prototype unit which had been tested in

Sweden; it operates on the basic principles of the AGA fog detector. In the AGA

visibility meter the axes of the projector beam and the receiver field of view are

one meter apart. Since the projector and receiver are housed in separate units,

the comparison beam from the projector is directed to the receiver by a fiberoptics light guide. The grey-scale of the instrument is rotated by a servo motor

to obtain a balance. A potentiometer is mounted on the shaft of the grey-scale

to furnish a signal voltage for the recorder, corresponding to the balance of the

grey-scale. This visibility meter measures the backscatter from the region 20 to

700 feet in front of the unit. This equipment can be operated at any inclination

from the horizontal to 60 degrees. The emitter is designed to refract suitable amounts

of light towards the axis of the receiver optics —sometimes referred to as a tailored

beam—to obtain a response which is relatively uniform for each section of the

sampled volume.

The equipment was installed in an instrument shelter at the Areata Airport near

the transmissometer T-L2, from which the transmittances for evaluating the response

of the fog detectors is obtained. The equipment was put into operation and the calibration of the performance checked by representatives of AGA. The records show

great sensitivity to changes in atmospheric conditions down to visibilities of onehalf mile. The output is slightly affected by daylight conditions. After a few weeks

operation the output showed an instability, which was caused by roughness or poor

contact of the potentiometer from which the output signal is obtained. Shortly after

this potentiometer was replaced the performance deteriorated because the lamp had

dropped out of the base and was hanging by the filament leads, but was still operating.

After replacing the lamp the performance did not return to normal. At the end of

the quarter further repair work was awaiting instructions from AGA.

Slant Visibility Meter.

The slant visibility meter was reactivated to obtain data for evaluating the

response of the AGA visibility meter when the latter is operated at the higher inclination angles.

Fog Variability Studies.

The draft of the ‘‘Summary of Low Visibility Conditions at the Areata Airport”

was completed and forwarded for review. The report includes a 10-year summary

of hours with transmittance below 0. 5 over a 500-foot baseline, a two-year tabulation

of runway visual ranges (RVR) below 1000 feet and below 800 feet, and a five-year

6

summary of FAA observations of low-ceiling and low-visibility conditions. The

report should be issued soon.

The instrument flight rule (IFR) conditions and the amount of time the runway

lights were operated at 100 percent (Step 5) intensity are recorded by elapsed time

meters. The hours of each for January, February, and March and for the entire

1967 year are as follows:

Quarter 1967

Instrument flight rules (IFR) 367 hours 2110 hours

Runway lights at step 5 intensity 30 hours 231 hours

A check of the records for T-D transmissometer showed the following hours of

low visibility conditions for the year 1967:

Transmittance below 0. 5 —daytime 150 hours

Transmittance below 0. 5 --nighttime 458 hours

RVR below 1000 feet —daytime 29 hours

RVR below 1000 feet —nighttime 17 hours

RVR below 800 feet —daytime 6 hours

RVR below 800 feet —nighttime 0 hours

Transmissometer Scattered-Light Error.

The measurements to determine the amount of light from the transmissometer

projector that is seen by the receiver after scattering are summarized in a Memorandum Report, “Scattered-Light Errors in Transmissometer Measurements.”

The error for several values of transmittance are given for receiver field of view

half-cone angle —of 9. 2, 12, 18, 25, 31, and 62 milliradians. Also a table showing

the error in indicated visibility in daytime resulting from this scattered light error

is given.

Transmissometers.

The Memorandum Report of Transmissometer Indicator Zero Shifts has been

issued. Information on the gradual down-scale of the ZERO reading of some transmissometer indicators during conditions with low transmittances are discussed. To

reduce these zero shifts a replacement of a bathtub type capacitor with a type having

low charge retention and a slight modification of the RC smoothing circuit of the

indicator voltmeter section are recommended.
I
7

III. AIRFIELD LIGHTING AND MARKING

Field Tests of Type L-842 Inset Runway Lights with Forced Drainage

Modification.

The five type L-842 inset runway lights, which are on continuing field tests

at Areata, were opened for inspection after eight months of operation. This was

during the rainy season. Water was poured over the lights while they were energized

and also shortly after turnoff on the day of the inspection to simulate rain continuing through a period of operation. After cooling to the natural temperature

the lights were opened and examined. Both the unmodified units and one of the units

modified for forced drainage were dry and showed no evidence of corrosion or

moisture. One of the modified units had a few drops of water in it and marks

showing that on occasions it had contained greater quantities of water. The other

modified unit had water covering the lamp and showed considerable corrosion. All

units were reinstalled without removing the water. Next day, after operating for a three hour period and cooling off, the lights were again examined and all units were

without water and the cavities were nearly dry. Apparently the forced drainage

modification will remove the water that may accumulate if the light is operated

continuously for three hours, but the light may tend to suck in water during the

cooling period.

Airfield Lighting Connector Field Tests.

Leakage current measurements were made on the 13 airfield lighting cable

connectors buried at the Areata Airport for continuing tests. These connectors

have been buried for more than eight years. These leakage current measurements

were made near the end of the rainy season. Eight of the connectors showed a slight increase in leakage. Leakage of three connectors had increased by a factor

of two. Two of the connectors had no appreciable change.

Field Tests of Cable- Fault Locator Developed by NBS.

The cable-fault locator developed by NBS has been tested on many circuits at the Areata Airport by locating faults and tracing circuits. This equipment performs

better than the AN/TSM-11 cable test-detecting set. Tracing series circuit cables

with the new NBS cable-fault locator is easy and accurate. Direct-burial cable is eas}^

to trace. Cables in metallic-duct or with an armor sheath can be followed, but

greater care is required. In locating ground faults the NBS unit can locate shorts to

ground within a few inches. Fairly high resistances to ground can be located also,

but the limit on high resistance faults has not been determined. In circuits with

8

multiple high-resistance faults usually several faults could be located, but those

which were located would have to be repaired before other faults on the circuit

could be located. A primary advantage of the NBS fault locator over the AN/TSM-11

in locating ground faults was the availability of another test frequency for use when

interference was a problem. The NBS fault locator can be used to follow the

circuit to within 100 feet or less of an ungrounded open fault. By tracing an open

circuit from both ends the approximate location of the ungrounded open fault

could be determined. The NBS cable-fault locator can be used to determine the

depth of direct burial cable very accurately by measuring the distance the detecting

element must be raised above the ground to decrease the reading to one-half value.

A progress report is being prepared on testing this cable-fault locator and should

be issued soon. Testing of this equipment will be continued.

Type L-8 52 Wide-Angle Airport Taxiway Light.

One type L-852 bidirectional wide-angle airport taxiway light was received

for test on February 6, 1968. The lamp used is a 65-watt Q65T2-1/2/1CL

halogen-cycle lamp in a prefocused mount. The light met the isocandela re- quirements of the specification (L-852) in both directions. The light has provision for inserting two colored glass filters, but none was used for the test. NBS Test Report 212. 11-3/68 will be issued.

Lights for Marking Transmission Lines and Their Supporting Structures .

A neon catenary light and a pair of condenser-discharge obstruction lights

(a “master” unit with a timing circuit and a “slave” unit) were received from

the Bonneville Power Administration, Portland, Oregon, for test.

Before the catenary light was tested it was found that a similar unit had been

tested in 1955. That unit had an intensity of 70 candelas in a particular direction

with a primary magnetomotive force of 1000 ampere-turns, and 35 candelas

with 500 ampere-turns. The present unit, with one measurement in the same

direction, had an intensity of 32. 5 candelas with 500 ampere-turns.

Only the master c-d obstruction light was tested. With 118 volts applied

the effective intensity (in the horizontal direction of the handle on the unit) was

above 1160 candelas between 5° and 10° vertical and increased from 130 candelas

to 1180 candelas from 0° to 5° vertical. The flashtube power was 12. 5 wattseconds per flash (at 42 fpm) for each flashtube.

)

9

Neon Obstruction Lights.

A neon obstruction light manufactured bjr Nelson Lights, Los Angeles, was

tested (1) with the red lens (an AN 2541-12 globe) which came with the light,

(2) with a clear lens (an AN 2 541-11 globe) and (3) with no lens. At 120 volts

input, between 2. 5° and 12. 5° vertical in one vertical distribution, intensity fell below the 32. 5 candelas reauirement of FAA Specification L-810: the minimum

intensit\^, with the red lens was 16. 0 candelas, with the clear lens, 21. 5 candelas

and with no lens, 23. 5 candelas. NBS Test Report 212. 11-1/68 was issued.

A second neon obstruction light (from an unknown manufacturer) was supplied

by the FAA for test. The neon tube is a five-turn spiral 4-inches in diameter and

9-inches in height. At 120 volts input the intensity in the region between 2. 5°

and 12. 5° vertical at some angles of azimuth fell to 26 candelas, below the 32. 5 candela reauirement of FAA Specification L-810. NBS Test Report 212. 11-2/68 was

issued.

Centerline Lighting for SATS.

Photometric measurements were made on two of the four SATS centerline

lights described in NBS Report 9694. One of the lights measured contains 75

type 715 lamps encased in three clear tygon tubes. The other three lights contain

39 type 715 lamps encased in three translucent poljmthylene tubes. Intensity

comparison of the two types of units is shown in Figure 1.

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10

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11

IV. CARRIER LIGHTING AIDS

Criteria for the Inspection of Fresnel Lenses.

A task was established for determining criteria for the inspection of

Fresnel lenses. Several lenses were received from the Naval Air Engineering

Center, Philadelphia. The lenses had all been rejected as unfit for service

by that organization but there was no evidence that the lenses were operationally

unfit for service or even if some of the criteria used for rejecting the lenses

would prove critical in an operational situation.

Some work was done with the lenses to determine if a measure of the stray

light, say at 1° off the peak of the beam, could be used as a criterion. Since

there was no lens available which had been judged operationally good, the results

of the tests were inconclusive. There were differences in the amount of stray

light of the lenses tested but these differences were largely not apparent when

the lenticular lens was installed on the cell, as this lens adds a substantial amount

of stray light in the direction of measurement.

12

V. MISCELLANEOUS TECHNICAL AND

CONSULTIVE SERVICES

The following proposals, draft reports and specifications have been reviewed.

Comments have been forwarded by letter, marked copy of the document, and/or

conferences with cognizant DOD and FAA personnel.

Heliport Lighting Test Program

FAA Specification 1100 “Photometric Procedures for CondenserDischarge Lamps”

Interim Report “Transmissometer Calibration Techniques and

Devices”

Purchase description for DF OLS. NAEC-MISC-08637. ID No.

80020.

VI. MISCELLANEOUS

Project Foggy Cloud.

A group from China Lake Naval Weapons Center has set up Project Foggy

Cloud at the Areata Airport. The purpose of Project Foggy Cloud is modification

of fog and low stratus by seeding. The seeding is planned to be accomplished by

airborne pyrotechnics, ground burns, and air drops of liquids and powders. A

wide variety of chemical compositions is to be tested. The evaluation of effective- ness is to be determined from airborne meteorological measurements, photography,

and visual observations. Originally the plans were to operate for only four or

five weeks during the spring and perhaps return, for more work during the fog

season, but this was changed to a continuing operation through the fog season.

>
11