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--- atmos:535:projects:lufft_r2s_precipitation_sensor [2008/12/13 01:01] – mphillips
+++ atmos:535:projects:lufft_r2s_precipitation_sensor [2020/01/29 17:25] (current) – external edit 127.0.0.1
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+======== Lufft R2S (Radar Rain Sensor) =========
+{{:atmos:535:projects:R2S_image.png}}
+      * Dimensions: (diameter x length) 90mm x 220mm
+      * Weight: approximately 4.5 kilograms
+      * Black aluminum sensor housing
+      * Heated plastic dome
+      * Easy installation
+==== Features ====
+      * Maintenance free precipitation sensor
+      * Differentiation between rain / snow
+      * Determination of quantity (1mm, 0.1mm, 0.01mm)
+      * Interface: RS485 and 2 digital outputs
+      * Can be configured for replacing tipping bucket systems
+==== Storage and Operating Conditions ====
+      * Storage temperature: -40°C to +70°C
+      * Relative humidity: 0 to 100% RH
+      * Operating temperature: -40°C to +60°C
+      * Relative humidity: 0 to 100% RH
+==== Installation Procedures ====
+{{:atmos:535:projects:Installation.png}}
+      * Sensor can be provided with shield if required distances not met.
+==== Connections ====
+      * There is an 8-pole screw-in connector on the underside of the device.
+      * This serves to connect the power supply and the interfaces using the associated connection cable.
+{{:atmos:535:projects:Connections.png}}
+      * 1 negative power supply
+      * 2 positive power supply
+      * 3 RS485_A
+      * 4 RS485_B
+      * 5 not assigned
+      * 6 Uout1
+      * 7 GND reference potential for the digital outputs
+      * 8 Uout2
+==== Interface ====
+      * Data bits: 8
+      * Stop bit: 1
+      * Parity: none
+      * Settable baud rates: 1200, 2400, 4800, 9600, 14400, 19200, 28800, 57600
+      * 19200 is factory setting and baud rate for firmware update
+==== Electrical Data ====
+      * Power supply: 20 to 30 VDC; typically 24 VDC
+      * Power consumption: < 100 mA (heating off)
+      * Heating duty 30VA
+      * Protection class: III (SELV)
+==== Digital Outputs ====
+      * The Uout1 and Uout2 digital outputs are short-circuit proof high side switches (12V) with integrated pull-down resistors.
+      * Possible configurations for Uout1 are:
+         * Tipping bucket simulation with 1mm, 0.1mm, or .01mm resolution
+         * Length of the output pulse for this simulation is typically 50 milliseconds
+      * Type of precipitation is transmitted on output Uout2 in the form of different frequencies.
+^ Precipitation Type     ^ Frequency/Hz      ^
+| Dry    | 0    |
+| Rain   | 10   |
+| Snow   | 20   |
+| Sleet  | 30   |
+| Freezing Rain  | 40   |
+| Hail   | 50   |
+      * If accumulated precipitation quantity is greater than 0.01mm, the frequency signal is transmitted for 2 minutes.
+      * The output of the frequency signal is maintained if a precipitation quantity greater than or equal to 0.01mm is measured within 2 minutes.
+==== Configuration ====
+{{:atmos:535:projects:Configuration.png}}
+      * Factory setting
+            * Device ID: 1
+            * Baud rate: 19200
+            * RS485 protocol: binary
+      * ID must be changed if several R2S devices are operated in a UMB network.
+      * **Drizzle detection**:
+            * When activated, measurement takes place with greater sensitivity.
+            * Identifies water droplets with a diameter of 0.3mm.
+            * The only disadvantage is that the high sensitivity may cause a slightly higher water quantity to be measured.
+      * **Hail detection**:
+            * If hail detection is activated, the side shield must be installed in all cases.
+            * The measurement signal reacts to movements (e.g. trucks) of up to 72 km/h
+            * Movements are interpreted as precipitation.
+            * Since the fall speed is identical, very large water droplets may be interpreted as small hail
+      * **Evaporation per day**:
+            * Simulate the natural evaporation of a tipping bucket
+            * A defined value is deducted from the rainfall quantity every minute.
+            * This is set at 0.24mm per day in the delivered condition.
+      * **Rainfall, Snowfall, and Hail correction factor**:
+            * The water quantity is assessed with this factor.
+      * The three particle types (rain, snow and hail) are added together and the precipitation type is assessed every minute.
+      * Requests 1-4 are carried out.
+      * They only take place if previous conditions are unfulfilled.
+      * __The factors cannot be changed__.
+) Number of hail particles per minute > 40% (Hail factor)
+      * Precipitation type = Hail
+) Number of rain particles > 90% (Freezing Rain factor) and ambient temperature <= 0°C
+      * Precipitation type = Freezing rain
+) Number of rain particles >20 % (Sleet factor) and ambient temperature in the range from –5°C to 4°C:
+      * Precipitation type = Sleet
+) Number of rain particles > 50% (Rain factor) :
+      * Precipitation type = Rain
+**If none of the 4 conditions is met but particles were measured, the precipitation type is snow.**
+      * Adjustment values:
+            * The range of the rain sensor measurement spectrum is from 130Hz (drizzle) to 1600 Hz (heavy rain).
+            * This range is divided into 23 zones, which can be individually corrected with factors from 0.1 to 10.
+==== Theory ====
+      * Doppler radars measure velocity by estimating the frequency-shift produced by an ensemble of moving targets.
+      * Doppler radars also provide information about the total power returned and about the spectrum width of the precipitation particles within the pulse volume.
+      * The reflected signal is the result of the energy from the transmitted pulse interacting with precipitation (snow, ice pellets, hail, and rain) particles.
+      * A small portion of the power is then returned to the radar and analyzed to determine an estimate of the rain or snow rate.
+      * The relationship between the size and power return is highly non-linear.
+            * An example is a very small, spherical drop.
+            * If you double the size of a the drop, you increase the reflected power return by a factor of 64.
+            * If you triple the size of the drop, you increase the reflected power return by a factor of 729.
+            * Polarimetric radars are designed to eliminate this problem.
+**Precipitation Rates**
+            * Example of two scenarios with identical rain rates:
+                  * Rain water concentrated in a very small number of large drops.
+                  * Rain water concentrated in a very large number of small drops.
+                  * Reflected power returned to the radar is heavily weighted towards the largest drops.
+                  * If only using the returned power to estimate rain rate, you might end up with either a significant overestimation or a significant underestimation of the rain rate.
+            * Radar power returned from irregular shaped mixtures of precipitation types can get quite complicated.
+            * The rainfall rate (R) is a product of the mass content and the fall velocity in a radar volume.
+            * Precipitation rate depends on particle size distributions.
+            * The natural variability in drop-size distributions is an important source of uncertainty in radar measurements of precipitation.
+            * Precipitation is usually measured by using the Z-R relation:
+                  * Z = AR<sup>b</sup>
+                        * A and b are constants.
+                        * This relationship is not unique.
+                        * Many empirical relations have been developed.
+                        * Typical values for the index and exponent are A = 200, b = 1.60
+**Radar Equation**
+      * Pr = (C |K|<sup>2</sup> Z)/r<sup>2</sup>
+      *|K|<sup>2</sup> is the refractive index factor of the target
+      * r is the slant range from the radar to the target (meters)
+      * Z is the radar reflectivity factor (usually taken as the equivalent reflectivity factor Ze when the target characteristics are not well known), in mm<sup>6</sup> m<sup>-3</sup>.
+      * C is the radar constant.
+**Attenuation**
+      * Attenuation by hydrometeors can result from both absorption and scattering.
+      * It is dependent on the shape, size, number and composition of the particles.
+      * Attenuation is dependent on wavelength.
+      * At 10 cm wavelengths, the attenuation is rather small while at 3 cm it is quite significant.
+      * Wavelengths below 5 cm are not recommended for good precipitation measurement except for short-range applications.
+      * The attenuation is dependent on water mass of the target.
+      * Ice particles attenuate much less than liquid particles.
+      * Snow or ice particles (or a hailstone) can grow to a size much larger than a raindrop.
+**Radar Wavelength**
+^ Band     ^ Frequency      ^ Wavelength      ^
+| UHF    |300-1000 MHz    | 1-0.3 m      |
+| L   | 1-2 GHz   | 30-15 cm      |
+| S  | 2-4 GHz   | 15-8 cm      |
+| C  | 4-8 GHz  | 8-4 cm      |
+| X  | 8-12 GHz  | 4-2.5 cm       |
+| K   | 18-27 GHz   | 1.2 – 0.75 cm      |
+      * The larger the wavelength, the greater the cost of the radar system.
+      * This is due both to an increase in the amount of material and to the difficulty in meeting tolerances over a greater size.
+      * Bands of weather radar interest include S, C, X and K.
+      * The sensitivity or ability of the radar to detect a target is strongly dependent on the wavelength.
+      * For the same antenna, the target detectability increases with decreasing wavelength.
+      * The shorter wavelengths provide better sensitivity.
+      * The disadvantage is that the smaller wavelengths have much larger attenuation.
+==== Field Work ====
+      * The Surface Transportation Weather Research Center (STWRC), along with the North Dakota Department of Transportation, established the STWRC Road Weather Field Research Facility (RWFRF) in late 2006.
+      * The purpose of this site is to understand better the physics associated with the interactions between the atmosphere and the roadway.
+{{:atmos:535:projects:Precipitation.png}}
+      * All observations are presented in 1-minute intervals.
+      * Evaluates the performance of the precipitation sensor.
+      * Provides monitoring of precipitation events.
+      * **Road Weather Field Research Topics Online:**
+            * Overview of the facility
+            * Field Site Data
+            * 24 hour Observations
+                  * http://stwrc.und.edu/timeplot/rwfrf.html
+            * Pavement Condition Model Validation
+            * Lufft R2S Observed Precipitation
+            * RWFRF Camera Images
+==== Maintenance/Cost ====
+      * Service and maintenance is carried out by a trained specialist.
+      * The recommended service interval is 12 months.
+      * The device must be disconnected from the power supply.
+      * Estimated cost for Lufft R2S system:
+            * $3000-4000
+==== Calibration ====
+      * The device is calibrated in the factory.
+      * The recommended calibration interval is 24 months.
+      * An onsite calibration service is available on enquiry.
+      * Testing of the signal processor with known artificially generated signals.
+      * Doppler calibration includes verification and adjustment of phase stability using fixed targets or artificial signals.
+      * The presence or absence of echoes from fixed ground targets may also serve as a crude check of transmitter or receiver performance.
+==== References ====
+      * Lufft R2S Precipitation Sensor Manual. 2006.
+      * __RADAR for Meteorologists.__ Rhinehart. 2004.
+      * Surface Transportation Weather Research Center.  http://stwrc.und.edu/.  2008.