atmos:535:projects:csat3_3-d_sonic_anemometer
Differences
This shows you the differences between two versions of the page.
Both sides previous revisionPrevious revisionNext revision | Previous revision | ||
atmos:535:projects:csat3_3-d_sonic_anemometer [2008/12/04 17:35] – jnaylor | atmos:535:projects:csat3_3-d_sonic_anemometer [2020/01/29 17:25] (current) – external edit 127.0.0.1 | ||
---|---|---|---|
Line 1: | Line 1: | ||
+ | ====== Sonic Anemometer ====== | ||
+ | * Manufacturer - Campbell Scientific | ||
+ | * Model Number - CSAT3 | ||
+ | {{: | ||
+ | |||
+ | |||
+ | ===== Description ===== | ||
+ | ==== Cost ==== | ||
+ | **Purchase**: | ||
+ | **Maintenance**: | ||
+ | **Calibration**: | ||
+ | |||
+ | |||
+ | ==== Operating Physics ==== | ||
+ | The main principle of a sonic anemometer is that the velocity of a sound wave in a moving medium is equal to the sum of the speed of sound and the velocity of the medium. | ||
+ | |||
+ | In the CSAT3, three sets of transducers are aligned non-orthogonally to one another (Figure 1). An ultrasonic impulse is sent between the transducer pairs. | ||
+ | {{: | ||
+ | Once each set of transducers has determined a wind speed along their axes, these wind speeds are converted into the u, v, and w components by multiplying the measured wind speeds by a 3 x 3 coordination transformation matrix. \\ | ||
+ | The CSAT3 makes a measurement when triggered by either the internal trigger or by an external trigger via a communication device. | ||
+ | {{: | ||
+ | Figure 1. Overview of the CSAT3 Sonic Anemometer | ||
+ | |||
+ | ==== Performance ==== | ||
+ | **__Measurement Rate__** \\ | ||
+ | 1-60 Hz \\ \\ | ||
+ | **__Resolution__** \\ | ||
+ | u and v component: 1 mm s< | ||
+ | w component: | ||
+ | speed of sound: | ||
+ | **__Operating Range__**\\ | ||
+ | -30 to 50 C (standard)\\ | ||
+ | -40 to 40 C (cold shifted)\\ \\ | ||
+ | **__Error (wind speeds < 30 ms< | ||
+ | u and v component < 4 cm s< | ||
+ | w component < 2 cm s< | ||
+ | |||
+ | **__Power Requirements__**\\ | ||
+ | Voltage: 10-16 V \\ | ||
+ | Power: | ||
+ | |||
+ | {{: | ||
+ | Figure 2: CSAT3 power requirements as a function of sampling frequency. \\ | ||
+ | |||
+ | ==== Field Projects ==== | ||
+ | Two examples of field projects utilizing the CSAT3 are given below. \\ | ||
+ | * Monitoring greenhouse gas fluxes over Korean rice paddies during the summer of 1999. \\ | ||
+ | * Retrieval of canopy turbulence profiles in and above Mediterranean tree crops (Figure 3). \\ \\ | ||
+ | {{: | ||
+ | Figure 3: Example of data obtained from the Meditteranean turbulence study (Vogt et al. 2006). \\ | ||
+ | |||
+ | |||
+ | ==== Specifications ==== | ||
+ | **Physical Description: | ||
+ | Measurement Path Length: \\ | ||
+ | 10.0 cm vertical; 5.8 cm horizontal | ||
+ | Path Angle from Horizontal: 60 degrees \\ | ||
+ | Transducer: 0.64 cm diameter \\ | ||
+ | Transducer Mounting Arms: 0.84 cm diameter \\ | ||
+ | Support Arms: 1.59 cm diameter \\ | ||
+ | **Dimensions: | ||
+ | Anemometer head: \\ | ||
+ | 47.3 cm (l) x 42.4 cm (h) \\ | ||
+ | Electronics box: \\ | ||
+ | 26 cm x 16 cm x 9 cm \\ | ||
+ | **Weight:** \\ | ||
+ | Anemometer head: 1.7 kg (3.7 lb) \\ | ||
+ | Electronics box: 3.8 kg (8.4 lb) \\ | ||
+ | |||
+ | |||
+ | ==== Documentation ==== | ||
+ | Campbell Scientific' | ||
+ | |||
+ | |||
+ | |||
+ | |||
+ | ===== Calibration ===== | ||
+ | ==== Method ==== | ||
+ | |||
+ | The CSAT3 is calibrated over the range of -30 to 50 C for standard mode or -40 to 40 C for cold shifted mode. The CSAT3 may or may not make measurements outside of this range, and any measurements taken outside of this range will be suspect. | ||
+ | |||
+ | The unit will require calibration when the wind offsets are greater than the manufacturer' | ||
+ | |||
+ | ==== Sources of Error ==== | ||
+ | One of the most problematic sources of error arises when the transducer pairs are obstructed or partially obstructed. | ||
+ | Another source of error that should be considered is the effect of a cross wind on measurements. | ||
+ | |||
+ | |||
+ | |||
+ | |||
+ | ==== Exposure Requirements ==== | ||
+ | The unit should be set up such that the anemometer is aligned with the prevailing winds. | ||
+ | |||
+ | |||
+ | |||
+ | |||
+ | |||
+ | ===== Deployment ===== | ||
+ | ==== Measurement Methods ==== | ||
+ | The CSAT3 can measure the following items: | ||
+ | * average horizontal wind speed | ||
+ | * average horizontal wind direction | ||
+ | * turbulent fluctuations of horizontal and vertical wind | ||
+ | * horizontal and vertical momentum flux | ||
+ | * sensible and latent heat fluxes | ||
+ | |||
+ | ==== Sampling Modes ==== | ||
+ | //**Single Measurement Mode**// \\ | ||
+ | In this measurement mode, the CSAT3 makes one measurement per trigger. The downfall of this approach is that high frequency signals are aliased to lower frequencies.\\ | ||
+ | // | ||
+ | Several measurements are taken for each trigger. | ||
+ | |||
+ | |||
+ | |||
+ | |||
+ | ==== Deployment Platforms ==== | ||
+ | ==== Communication ==== | ||
+ | The CSAT3 has three ouput signals: SDM, RS-232 (serial), and analog. | ||
+ | |||
+ | ==== Power and Installation ==== | ||
+ | The CSAT3 should be installed such that it points towards the prevailing wind. This technique will help minimize contamination errors from the arms of the instrument as well as other supporting structures. | ||
+ | The CSAT3 has a bubble level on the anemometer head to aid in leveling the instrument. | ||
+ | |||
+ | ==== System Automation ==== | ||
+ | The CSAT3 is designed to support automation. | ||
+ | {{: | ||
+ | Table 1: SDM compatible dataloggers. | ||
+ | |||
+ | |||
+ | |||
+ | |||
+ | |||
+ | ===== Data ===== | ||
+ | |||
+ | |||
+ | |||
+ | ==== Quality Control ==== | ||
+ | The CSAT3 has a built in algorithm that corrects for the effects of crosswinds on the wind measurements. | ||
+ | |||
+ | ==== Quality Assurance ==== | ||
+ | Some quality assurance measures that may need to be taken with the CSAT3 would be to remove data collected during precipitation events, as the precipitation would interfere with the ultrasonic signal. | ||
+ | |||
+ | ===== References ===== | ||
+ | http:// | ||
+ | |||
+ | Liu, H., Peters, G., and Foken, T.: 2001, "New Equations for Sonic Temperature Variance and Buoyancy Heat Flux with an Omnidirectional Sonic Anemometer", | ||
+ | |||
+ | www.atm.helsinki.fi/ |