What are the advantages and disadvantages of Disdrometer for determining rain drop size distribution? And how about other methods like high-speed imaging or etc.? Which methods do you prefer if Disdrometer is not available?
Dear Zahra,
The following text was taken from a recent review article entitled "Rain Drop Measurement Techniques: A Review " published in Water (MDPI) which illustrates all available methods, their scope and limitations.
Automated Rain Drop Measurement Techniques
Impact Disdrometers
The kinetic energy of rain drops is critical to soil erosion and stormwater pollutant wash off studies because it is indicative of the potential of drops to displace particles normally bound to a surface, causing to soil particles to enter surface water flows. The combination of drop size distribution and drop velocity can provide an estimation of kinetic energy, however there have been several previous attempts to take measurements directly. This has been done using either acoustic or displacement methods.
Acoustic Disdrometers
Acoustic disdrometers involve the generation and recording of an electric signal via a piezoelectric sensor when drops fall on a specialized diaphragm. Based on the relationship between kinetic energy and drop size calculations, this electrical signal is converted to kinetic energy via the measured acoustic energy. Modifications to the sensors used in acoustic disdrometers by Nystuen et al. enabled use
in marine environments, however difficulties remained during high rainfall intensity measurement. Jayawardena and Rezaur also successfully modified the acoustic disdrometers, and improved drop size distribution, rain intensity and kinetic energy measurement accuracy. Other commercial devices have been successfully developed by Salmi and Ikonen [97], Salmi and Elomaa, Winder and Paulson, Bagree and Vaisala.
Limitations to accuracy in drop size estimation arise using acoustic disdrometers due to the difficulty in obtaining a uniform acoustic response over the entire diaphragm. Difficulties in the accurate measurement of smaller drop sizes also remain because of insensitive diaphragms, and splash effects. In addition, higher intensity storms are not able to be measured due to background noise which decreases measurement accuracy.
Displacement Disdrometers
Energy generated by drops falling on the top surface of a displacement disdrometer is translated via magnetic induction, and converted via electrical pulse to estimate the size of a rain drop. In addition to magnetic induction, several mechanisms have previously been trialled to accurately measure drop size including elastic springs, bonded strain gauges, and pressure transducers. Arguably the most widely used displacement disdrometer is the Joss-Waldvogel Disdrometer which has been commercially available for past 45 years. This unit has undergone several iterations to improve the composition of the cone which is the principle measurement component. Successful modifications have included the addition of a digital converter. Although this disdrometer may have provided advantages such as measurement over a wide range of drop sizes, and the ability to continuously sample over longer durations, limitations remain including accurate drop counting, and accurate measurement of velocity, kinetic energy, intensity, and drop shape.
Optical Disdrometers
Optical technologies (optical imaging or optical scattering) are non-intrusive rain drop measurement techniques. These methods do not influence drop behaviour during measurement, and have successfully resolved drop break up, and drop splatter problems experienced by other measurement methods.
Optical Imaging
Recent imaging techniques developed have involved two motion cameras (2DVD) to show raindrop microstructure, including front and side drop contours, fall velocity, drop cant and horizontal velocity. General rainfall parameters such as rain intensity and drop size distributions have also been accurately measured. Two motion cameras record images of drops which have been used to accurately measure drop velocity, diameter, and shape (including oblateness. Measurement errors arising from drop drift caused by the tall unit design have led to design modifications, including the development of an indoor model, and one specifically designed for outdoor use. Liu et al. developed a video system capable of accurate drop shape and velocity measurement. The set up consists of optical and processing units, and a unique imaging unit comprised of a planar array charge-coupled device sensor (CCD).
For the other methods, please see attached file.
Hoping this will be helpful,
Rafik
- Badges
- Science topic
- Similar topics
- Geoscience
- Atmospheric Sciences