5,838
edits
Rain measurement: Difference between revisions
From Cumulus Wiki
Jump to navigationJump to search
m
→Webtags report: make clear the main screen also shows 'this season'
m (→Rain Gauge Location: text added here that was previously in faq) |
m (→Webtags report: make clear the main screen also shows 'this season') |
||
| (14 intermediate revisions by the same user not shown) | |||
| Line 9: | Line 9: | ||
= Precipitation measurement and Cumulus = | = Precipitation measurement and Cumulus = | ||
Cumulus processes rainfall in one of two [[cumulus.ini| units]] (millimetres and inches). Most processing by Cumulus is based on the total rainfall count output by a weather station, see [[FAQ#My_station_invented_some_rain_that_didn.27t_really_occur.2C_and_I_want_to_set_it_to_zero_.28or_some_other_figure.29 | FAQ]] for more. The rainfall observations output by different weather stations varies, see [[Monthly_log_files]] for the parameters that Cumulus tracks. Cumulus can also read rainfall from a separate RG11 optical gauge. | Cumulus processes rainfall in one of two [[cumulus.ini| units]] (millimetres and inches). Most processing by Cumulus is based on the total rainfall count output by a weather station, see [[FAQ#My_station_invented_some_rain_that_didn.27t_really_occur.2C_and_I_want_to_set_it_to_zero_.28or_some_other_figure.29 | FAQ]] for more. The rainfall observations output by different weather stations varies, see [[Monthly_log_files]] for the parameters that Cumulus tracks. Cumulus can also read rainfall from a separate RG11 optical gauge. | ||
== Rain day == | |||
The threshold value which the daily rainfall has to equal or exceed for the day to be considered a 'rain day' is set in [[Cumulus.ini#Section:_Station | RainDayThreshold]] and has a default value of ''-1'' that means 0.2mm or 0.01in. Alternative thresholds can be used by specifying a number in the units your configuration uses. | |||
== Cumulus View Menu == | |||
=== Highs and Lows === | |||
On the Cumulus '''View''' ''Highs and lows'' screens you can see those of the following appropriate to the chosen period: | On the Cumulus '''View''' ''Highs and lows'' screens you can see those of the following appropriate to the chosen period: | ||
* Highest Hourly/Daily/Monthly Rainfall | * Highest Hourly/Daily/Monthly Rainfall | ||
* High | * High [[#Rain_Rate|rainfall rate]] | ||
* Longest wet period (count of consecutive days with rainfall above configured threshold) | * Longest wet period (count of consecutive days with rainfall above configured threshold) | ||
* Longest dry period (count of consecutive days with rainfall below configured threshold) | * Longest dry period (count of consecutive days with rainfall below configured threshold) | ||
All of these values are also available from [[Webtags]]. | |||
[[Webtags]] report | === ''This month/period/year'' screens === | ||
* For current, | A number of values are shown for rainfall, these are calculated by summing field 14 (total rain today) from relevant rows in [[dayfile.txt]] (so will exclude the current meteorological day): | ||
* For today, yesterday, this month, this | # Total rainfall | ||
* Snow depth for current day | #* Total for this (any) month | ||
#* Total for this (any) period you want (select start date and end date) | |||
#* Total for this (any calendar) year is shown on 'This year' screen | |||
# Wettest day (equivalent to 'Highest Daily Rainfall' parameters of webtags) | |||
# High [[#Rain_Rate|rainfall rate]] | |||
# Rain days (count of days in period with rainfall above configured threshold) | |||
# Dry days (count of days in period with rainfall below configured threshold) | |||
# Days in period with snow falling (from [[Weather_Diary]]) | |||
# Days in period with snow lying | |||
==[[Webtags]] report == | |||
* For current, last 24 hours, yesterday (<#rfallY>), and this month; | |||
**totals (<#rfall>, <#r24hour>, <#rmonth> all include rainfall so far today) | |||
* Annual rainfall web tag <#ryear> reports total for ''rainfall season'' year i.e. starting month set on Configuration | station screen | Annual rainfall frame; includes rainfall so far today, same figure as shown for 'This year' on main Cumulus screen) | |||
* For today, yesterday, this month, this rainfall season, month-by-month, and all time; | |||
** hourly rainfall highs and timestamp, | |||
** daily rainfall highs and timestamp, | |||
**rain rate high | |||
* Snow depth for current [[Weather_Diary#How_do_I_change_the_time_a_diary_day_begins.2Fends.3F|day]] | |||
* Longest wet period (count of consecutive days with rainfall above configured threshold) | * Longest wet period (count of consecutive days with rainfall above configured threshold) | ||
* Longest dry period (count of consecutive days with rainfall below configured threshold) | * Longest dry period (count of consecutive days with rainfall below configured threshold) | ||
* Timestamp of last rain gauge tip (and, from version 1.9.4, how many days ago) | * Timestamp of last rain gauge tip (and, from version 1.9.4, how many days ago) | ||
* <#IsRaining> | * <#IsRaining> <#RG11RainToday> <#RG11RainYest> are available for Hydreon RG11 detectors only (the first applies to rain detection mode, the others apply to the tipping bucket mode) | ||
= Types of Rain Gauge = | = Types of Rain Gauge = | ||
| Line 55: | Line 66: | ||
The advantages of this type of gauge over tipping buckets are that it does not underestimate intense rain, and it can measure other forms of precipitation, including rain, hail and snow. These gauges are, however, more expensive and require more maintenance than tipping bucket gauges. | The advantages of this type of gauge over tipping buckets are that it does not underestimate intense rain, and it can measure other forms of precipitation, including rain, hail and snow. These gauges are, however, more expensive and require more maintenance than tipping bucket gauges. | ||
== Optical Rain | == Optical Rain Gauges == | ||
One design has a row of collection funnels. In an enclosed space below each funnel is a [http://en.wikipedia.org/wiki/Laser_diode laser diode] and a [http://en.wikipedia.org/wiki/Photodiode phototransistor detector]. When enough water has been collected to form a single drop it drips from the bottom of the funnel, falling into the laser beam's path. The detector is set at right angles to the path of the laser beam so that light scattered by the drop of water breaking the laser beam is detected as a sudden flash of light. The flashes from these photodetectors are then read and transmitted or recorded. | #One design has a row of collection funnels. In an enclosed space below each funnel is a [http://en.wikipedia.org/wiki/Laser_diode laser diode] and a [http://en.wikipedia.org/wiki/Photodiode phototransistor detector]. When enough water has been collected to form a single drop it drips from the bottom of the funnel, falling into the laser beam's path. The detector is set at right angles to the path of the laser beam so that light scattered by the drop of water breaking the laser beam is detected as a sudden flash of light. The flashes from these photodetectors are then read and transmitted or recorded. | ||
#The [http://www.rainsensors.com/| Hydreon Optical Rain Sensor] - Model RG-11 - uses an infrared sensor to detect rainfall with high precision. Some car windscreens have a similar sensor to automatically start wipers. Cumulus supports the RG11, via parameters in [[Cumulus.ini#Hydreon_specific:]] that are set using a RG11 screen within the configuration menu. Use a USB to RS232 (serial) adapter on computers which don't have a COM port. See Cumulus ''help'' for more information. The rain sensor's 'normally open' relay contacts should be connected via a serial port (9 way connector) | |||
The [http://www.rainsensors.com/| Hydreon Optical Rain Sensor] - Model RG-11 - uses an infrared sensor to detect rainfall with high precision. Some car windscreens have a similar sensor to automatically start wipers. Cumulus supports the RG11, [[Cumulus.ini# | #*either to the Data Set Ready (pin 4) and Data Terminal Ready (pin 6), | ||
#*or to the Request To Send (pin 7) and Clear To Send (pin 8)]. | |||
#*You can connect two RG-11 sensors to the same port, one to DSR/DTR and one to RTS/CTS (one has to be in "It's raining" mode and one in "tipping bucket" mode). | |||
=Rain Gauge Location= | =Rain Gauge Location= | ||
The exposure of a rain gauge is very important for obtaining accurate measurements. As a general rule, the windier the gauge location is, the greater the precipitation error will be. You can find lots of discussions online about wind effects, and rain shadows, together with research on positioning requirements in rural and urban locations. A good starting point is [http://www.rmets.org/weather-and-climate/observing/guidelines-observing-0 this UK website]. | The exposure of a rain gauge is very important for obtaining accurate measurements. As a general rule, the windier the gauge location is, the greater the precipitation error will be. You can find lots of discussions online about wind effects, and rain shadows, together with research on positioning requirements in rural and urban locations. A good starting point is [http://www.rmets.org/weather-and-climate/observing/guidelines-observing-0 this UK website]. | ||
Gauges should not be located close to isolated obstructions such as trees or buildings, which may deflect precipitation due to erratic turbulence. To avoid wind and resulting turbulence problems, do not locate gauges in wide-open spaces or on elevated sites, such as the tops of buildings. | Gauges should not be located close to isolated obstructions such as trees or buildings, which may deflect precipitation due to erratic turbulence. To avoid wind and resulting turbulence problems, do not locate gauges in wide-open spaces or on elevated sites, such as the tops of buildings. For a separate rain gauge (e.g. Fine Offset), experiment to find whether the best protection from the wind occurs with the buckets arranged to line up with the mast or at right angles to the supporting arm between gauge and mast. | ||
The WMO recommend that a rain gauge be placed away from any nearby obstacle a distance of at least twice the height of the obstacle. The best site for a gauge is one in which it is protected in all directions, such as in an opening in a grove of trees. The height of the protection should not exceed twice its distance from the gauge. | The WMO recommend that a rain gauge be placed away from any nearby obstacle a distance of at least twice the height of the obstacle. The best site for a gauge is one in which it is protected in all directions, such as in an opening in a grove of trees. The height of the protection should not exceed twice its distance from the gauge. | ||
