FI115927B - Procedure for compensating the contamination of the pane in the scope gauges - Google Patents

Description

115927

FIELD OF THE INVENTION The invention relates to a method for determining visibility at airports in particular. Such devices determine visibility according to the transmission or reflection characteristics of the atmosphere. These devices send and receive light pulses to derive the current visibility for a change in the intensity of the light pulse received over that measurement distance relative to the transmitted light pulses. Devices using permanent light are also used. One constant problem with such devices is that the screen placed in front of the transmitter or receiver is dirty. Screen contamination is due not only to atmospheric influences such as rain, snow and atmospheric dust particles, but also to increasing emissions from aircraft engines at airports, which contain relatively high levels of oil and gasoline mist. Reliable proof of visibility is strictly possible only on cleaned screens. This would require continuous maintenance work.

* · · • · · • f I »· ·:. ·. To solve this problem, it has already been proposed to position the blower, which may »» · prevent the deposition of dust particles. 25 squares (DE-PS 24 28 9019). Thus, complete prevention of contamination is ultimately not possible. The use of shields, shields and the like is also problematic, | because access to screens is difficult in service cases or continuous measurement is not possible. Finally, such ul. \ 30 mechanical parts usually require a lot of repair and maintenance.

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In order to extend the service intervals of the visibility meters, it is proposed to use a combination of at least one transmission meter and one scatter-35 interleaver.

115927 2 The essential power of this combination is that the atmospheric transmission approaches 100% with good visibility. The computational dependence is given in the known Koschmider formula: 5 MOR = In E x B / ln T (1) MOR = Meteorological optical range 10 E = slope threshold (eg 0.05) B = basic measurement length (eg 50 m) ) T = measured transmission value (%) As a result, with increasing visibility, the associated transmission change becomes smaller and smaller. On the other hand, the fouling of the device boxes reduces the measurement of the transmission by an absolute factor of 1 or 3%, depending on the fouling. This results in a dramatic reduction in measurement accuracy, especially with good visibility. Figure 1 illustrates 20 relative visibility measurement errors δ MOR / MOR along the standard length B of normalized visibility MOR with various high absolute coefficients such as screen fouling. For example, a visibility value of MOR = 2500 m can be found on the MOR / B axis for a measurement length of 50 m. Figure 1 illustrates;; ·. 25 guarantees this visibility value at only 0.3% absolute; coefficient (fouling) of a relative measurement error of 5%. This indicates that the transmissometer responds well; ; * very susceptible to soiling.

V '30 The situation is quite different in the case of scattering visibility meters, that is to say, in particular, devices which make use of forward or backward scattering. This can be demonstrated by the transmis- sion example of the basic equation (1). \ for a siometer with a measuring range ending in MOR = 2000 m 35 and using the values given in equation (1): • T * eA (In 0.05 x 50m / 2000m) = 0.927842; * · , · If a reliable ± 10% MOR measurement error is taken as the basis: • · 3 115927

Ttll = e ~ (ln 0.05 x 50m / 2200m) = 0.934181 T-μ = e ~ (In 0.05 x 50m / 1800m) = 0.920153 1 \ u - T = AThi = + 0.00633875 5 Ti, - T = δΤ-ιι = “0.00768898 The post-calibration with MOR = 10 km would be done with the following nominal value of the transfer: 10 T = e * (In 0.05 x 50m / 10000m = 0.985133) in a post-calibration linearly: 15 aT * = δΤη * x 0.985133 / 0.934181 * 0.0067 AT. = aT-m x 0.985133 / 0.920153 * 0.0082 Post-calibration to the measured measurement MOR = 10 km gives each of the following limits being tolerated: 20 T * 0.985133 + 0.0067 = 0.991833 T. = 0.985133 - 0.0082 = 0.976933 ... where equivalent visibility reference measurements are obtained,), 25 watts per 10 km to move at face value.

• · · 4: The MOR conversion of the Si values gives a comparison of visibility • · <! as possible limits for measured values:: Y: 30 M0R | = In 0.05 x 50m / ln 0.991833 = 18.2 km MOR. = In 0.05 x 50m / ln 0.976933 = 6.42 km «* · * · · ♦. ···, Especially the forward-scattering devices have good measure, no. With 10 km visibility,

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: 35 corresponds to better measurement accuracy. Therefore, with good visibility, the signal of the transmissometer can be:. ·, Be scanned by the measurement value of the scattering meter.

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It is possible to use a scattering interleaver constructed in accordance with the backscatter principle. However, the use of a forward scattering light meter is a priority.

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Particularly advantageous is the use of a scattering light measuring apparatus which, in itself, comprises compensation for screen contamination, such as, for example, the use of at least one internal receiver 10 directly opposite the transmitter. Such a measuring device is described in DE 44 01 755.3. It consists of one light source disposed in the forward scatter arrangement and at least another receiver disposed on the optical axis of the transmitter to determine transmission.

15 The transmitter and receiver are usually provided with peripherals for generating a suitable beam and windows to protect against environmental influences. Deposits accumulating on the windows result in a compensatory measurement error. By measuring with both the transmission and scattering light system, with the same measurement intensities (defined by the apertures of the light transmitter * and the scattering light receiver), it is possible to *. ·: Compensate for the effect of window contamination. Because observing events are very slow in time,; '· *: 25 could be received by both receivers during transmission and scattering}.'. In subsequent sub-measurements, a single interpreting electron can be obtained, in which case the scattering light must also be equipped with a pre-amplifier. . precipitation. Assuming that the windows of adjacent receivers * ;; _: 30 have the same dirt and that the displacement measurement "· '' arrangement is substantially distorted only by the absorbing effect of the tilt of the window li - ί · .., the measurement error caused by window contamination can be determined , or the ratio of the measured scattering amplitude to the measured transmission "35 gives a compensated, i.e., scattering-free" amplitude. In this case, the determination of the fouling of the individual screens is not relevant, but the fading of the scattering light screen is automatically compensated by the formation of each of the aforementioned 5 115927 measurement values. The principle structure of the combined visibility and rain measurement device according to the invention is shown in Fig. 2 in connection with the accompanying operating diagram. It means: 5 6) Measuring intensity 7) Receiving optics and instrument window E2 8) Optical narrowband filter 9) Receiving diode E2 10 with pre-amplifier groove 10) Amplifier with characteristic band-pass characteristic for transmission measurement E2, center frequency fm

13) LED Drive Electronics SI

14) Volume control, transmitter SI

15) Transfer LED SI

15 16) Receiving optics and device window El 18) Optical narrowband filter 19) Receiving diode E 21 with preamplifier Band-pass amplifier for beam measurement E2, center frequency fm 20 22) Modulation generator, frequency fm 14), 27) Scattering light E1 average generator 31) E2 averaging transducer t'ym 25 32), 35) Synchronous demodulator, 36) Microprocessor for monitoring and interpretation • · ·

37) Transmission Optics and Device Window SI

* ♦ i A Mean of scattering light E1 (visibility)> / · * 30 D Meaning of scattering E2 (offset) E Current value of scattering1 (rain): H Current value of scattering E2 (rain) 1 · · * ♦ il '** Measured values A and D include the mean of what-

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: 35 scattering amplitudes or measured offsets. The values i ,,, 1 can be input directly to the quotient generator or the like: using a memory and a calculator to calculate the quotient (36).

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The calculated, corrected scattering amplitude can then be calculated, taking into account the device-type vibration constant, to calculate the visibility value i.

5 In order to determine the type of rain, compensated amplitudes over time as well as the forward scatter signal and the transfer signal (instantaneous values E, H) can be used. A schematic representation of the scattering amplitude (ordinate of the logarithmic scale) shown in Figure 3 provides typical signal amplitudes and time costs for the individual 10 types of rain (rain, drizzle, hail, snow). The individual relative maxima of the scattering light are formed by modulation of the light source (LED, voltage passage after the receiver demodulator). As a result, the rain is illuminated many times during the passage of the measuring volume according to the principle of the stroboscope 15. From the number of scattered wave groups of modulated illumination, the velocity of rain can be deduced. Simultaneous monitoring of the transfer can determine the size of the droplets or particles that form rainfall from the known velocity of the rain drops, since the total sedimentation is expressed by the particle size of the observation volume, or a single volume can be deduced from the known velocity. Thus, by simultaneously measuring scattering and transfer, it is not possible to determine not only the quality of the rain, but also the amount of precipitation. (For special applications, the speed j can also be determined from the frequency shift of the scattered radiation with respect to the illumination frequency).

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Since the assumption that the fouling of both receivers is: 30 the same is not always the case, an extremely advantageous V · embodiment is provided with an additional transmitter. In this case, the transmitter and the receiver are facing each other in a • rectangular arrangement. The transmission and scattering measurement of individual illumination beams or reception beams can then be: '· 35 compensated by partial measurements.

The compensation procedure is schematically illustrated in Figure 4.

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In a first partial measurement, both transmission and scattering of radiation from transmitter S are measured when receiving E1 or at receiver E2. At the receiver E1, the transmission signal measured consists of transmitter S2 gain-5 and absorption or transmission through the optics of transmitter S2 and receiver E1. The scattering measurement determines the measured forward scattering of the scattering amplitude and absorption (or shift) of the measuring volume through the optics of transmitter S2 and receiver E2.

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In the second submeasure, the corresponding signals are detected in reverse order. Individual submeasures of transmission and scattering amplitude provide a corrected signal

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FSC = f FSC1 x FSC2 TRI x TR2

Partial measurements can be made over time, one after the other. The corresponding arrangement is schematically shown in Figure 5.

It means: * * ·:: 1) Transmitter S2 volume control 2) LED drive electron still • »: * · * .25 3) Volume control reference LED; . ·, 4) Transmitter LEDs S2 tt »* *; * _ 5) Transmitter optics and instrument window S2 i ·« 6) Measuring volume 7) Receiver optics and instrument window E2 «': 30 8) Optical narrowband filter. ** 9) Pre-amplifier receiving diode E2 _ 10) Bandpass characteristic amplifier for transmission measurement E2, center frequency fm 11) Bandpass characteristic amplifier for scattering: "35 light measurements E2, center frequency fm \ '·· 12) Scatter measurement switch

13) LED Drive Electronics SI

14) Volume control transmitter SI

8 115927

15) Transfer LED SI

16) Reference light diode for volume control 17) Receiver optics and device window E 18) Optical narrowband filter 5 19) Pre-amplifier counter-diode No 20 switch 23) transmitter S1 / S2 switch 24) modulation generator 25), 26) phase correction of the synchronous signal generation 27) average of the scattering light measurement 15 28) of the average of the transmission measurement 29), 30) for synchronous demodulator 31)

32) Transmitter optics and device window SI

20 A Average Scattering Light Measurement (Visibility): i; B Average of transmission measurement (compensation); '5'; C At the moment of scattering, 1 setpoint (rain) D Si at the moment of metering (setpoint) (rain) * (25

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! ! In the structure shown schematically in Fig. 6, it is also possible to carry out the first and second partial measurements I 1 · * 1 · when transmitter 1 and transmitter 2 are operated at different modulation frequencies (fa, fb) and receivers * · i 30 are located at respective modulation frequencies > 't: Tuned Interpretation Devices (32-35). Depending on the goodness and resolution of the reception amplifier; · ', the modulation frequencies ... must have a sufficient distance. It means: i; 1 ·· 35 1) Transmitter S2 Volume Control 2) LED Drive Electron Still 3) Volume Control Reference LED 4) Transmitter LED S2 9 115927 5) Transmitter Optics & Device Window S2 6) Measuring Volume 7) Receiver Optics & Device Window E2 8) 9) Receiver diode E2 with preamplifier 10) Filter with transmission bandwidth E2, center frequency fm 11) Amplifier with bandwidth measurement E2 bandwidth, center frequency fm

10 13) LED Drive Electronics SI

14) Volume control, transmitter SI

15) Transfer LED SI

16) Volume control reference light diode 17) Reception optics and device window El 15 18) Optical narrowband filter 19) Receiver diode with preamplifier E1 20) Transmission measurement El bandpass gain amplifier, center frequency fm 21) Frequency frequency gain E2frequency frequency bandwidth fa ί 23) Modulation generator, frequency fb,! ': 24), 25) Phase correction for synchronous signal generation 26), 27) ί \\ 25 28) Scatter light measurement E1 average generator * »•, -t 29) Transition measurement E1 average generator' i | 30) E2 mean of scattering light measurement 31) E2 mean of shift measurement 32), 33) Synchronous demodulator • i i 30 34), 35) V 5 36) Microprocessor for monitoring and interpretation

; 37) Send inopt i age and device window SI

i 'A Mean of scattering light E1 (visibility) “35 B Mean of scattering light E1 (compensation) • *; '· C Average Scattering E2 Mean (Visibility) D Scanning E2 Mean (Compensation) E Scattering E Current1value (Rain) 10 115927 F Scattering E1 Current Value (Rain) G Scattering E2 Current1value (Rain) H Transition Measurement E visibility meters to compensate for screen contamination will be described in connection with the exemplary embodiment shown in Figure 7.

A plurality of transmission meters 72, 10 73, 74 are disposed on the runway 71, these, such as the forward scatter measuring device 75, are connected by wires 77 to the junction unit 76. The junction unit 76 is connected by wire 78 to the interpretation unit 79. As soon as the forward scatter gauge , place this MOR value 15 in equation (3) above. It gives a transmission value of, for example, 98.5% with a 10 km visibility. This offset value is set to the hold value in the transmission and is used to indicate the offset to form a correction factor.

In particular, the transmission value calculated from the scattering light measurement relative to one or more transmitters e t t! I! to the transfer value of the assignment. This ratio then describes the correction factor which causes a measurement error of less than 10% at the end of the transmission range of the transmission (e.g. 2000 m).

As a result, under poor visibility conditions, * * * where transmitters typically exhibit better measurement accuracy of '* t than the scattering light dimension v t' * 9 'of Fig. 1, a significantly reduced measurement error is obtained.

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! -! ! The correction factor thus determined is multiplied by the respective indications of the transmission V: until better visibility conditions occur again. The new correction factor can then be redefined under good visibility conditions. This also results in a significantly reduced long-term maintenance interval for i * * · 35.

> i *% * * i In addition, the inverse value of the correction factor thus determined shows how large the level difference range still used for the displacement measurement is 11 115927. Accordingly, maintenance work (general screen cleaning) can be targeted. In addition, it occurs in the maintenance of individual transmission meters, esm. the possibility of performing a rough calibration of the individual or all transmitters with the visibility of the Siron-5 conventional measuring instrument when changing the transmitter. In this context, accurate post-calibration will be performed automatically in the next eventual weather event.

10 Finally, cleaned screens can be used to compare correction factors.

Other advantages of the combination of the transmission transmitters and scattering light meters of the invention are that, with the Siron-15 conventional measuring device, visibility values over two kilometers are also available, and that the scattering light measuring device also provides reliable measuring data on the type and accumulation of rain.

20 So far, since only the fouling of the screen has been mentioned, it is to be understood solely as, for example, the effects '· /' · which completely distort the measurements of the transmission. Such effects include, for example: • · 25 - inadequate calibration, e.g. , ·, Under visibility and weather conditions after touching the equipment ..V; - long-term extension stability of the transmitter and receiver units (concrete base stability, substrate stability / soil ·. :: 30 movements, general mechanical long-term stability for auxiliary V components); - the use of transmitting and receiving optics or electro », ···. long-term stability of bronchi (aging of light sources, • prolonged use of light intensity, light distribution, or: '' 35 receiver sensitivity).

5 1 1 5927 12 Such effects can be corrected by the apparatus and method disclosed, but cannot be corrected by conventional methods so far.

10 15 20 i ··: · 25: 30: “35

Claims (3)

Method for compensating the fouling of a box in a transmissometer for sight measurement, characterized in that at longer than 10 km's sight, the transmission is calculated on the basis of a scatter measurement obtained from a scatter light meter, and this value is installed as the transmission measurement. setpoint for calibrating the transmitter. Method according to claim 1, characterized in that in order to form a correction factor, the value obtained from the scattering light meter is placed in relation to the transmission specified by the transmitter meter. Method according to claim 2, characterized in that the measured values of the transmissometer are multiplied by the determined correction factor. 20 • · «# ·« · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · »* · • I» »►» »· • II» • I »» Il »»