Hydrology

Question No 1:

                  Which one is the most reliable data source to measure precipitation:

• RADAR Data • Satellite Data • On ground observatory (Meteorological Station) Precipitation

                           Precipitation is any liquid or frozen water that forms in the atmosphere and falls back to the Earth. It comes in many forms, like rain, sleet, and snow. Along with evaporation and condensation, precipitation is one of the three major parts of the global water cycle.

Forms of precipitation o Raindrops o Ice pellets o Hail o Snowflakes o Diamond dust Measurement

                              Today, scientists can measure precipitation directly using ground-based instruments such as rain gauges or indirectly using remote sensing techniques (e.g., from radar systems, aircraft, and Earth-observing satellites). 

1-Rain gauges:

                               Rain gauges measure precipitation amounts at a given location. Oftentimes measurements from an individual rain gauge are used to represent precipitation conditions across larger areas, i.e., between gauge sites. However, that is not always the best assumption. The reality is that precipitation may fall more- or less-intensely at the location of the gauge—or it may miss the gauge entirely

Demerits or Faults: I. Direction of Wind may affect the collection of precipitation II. Evaporation may also affect the value of the value of precipitation. III. some water is used to wet the surface of instrument 2-Radar:

                              Radar instruments can easily monitor rainfall over larger areas. Through indirect measurements weather radars also provide data of better spatial and temporal resolution. To take advantage of strengths and minimize weaknesses of rain gauge and radar measurements many methods were elaborated to merge gauge and radar data. There are two types of Radars which we used:

i-Doppler weather radar:

                                Doppler Weather radar is mostly used in the United States and it could measure the Doppler frequency shift in addition to the magnitude of the echo signal reflected from precipitation to measure precipitation value.

ii-Ground-based weather radars.:

                                  Ground-based radars send out pulses of microwave energy in narrow beams that scan in a circular pattern. When the microwave pulse encounters precipitation particles in the atmosphere, the energy is scattered in all directions, sending some energy back to the radar. These measurements are used to estimate intensity, altitude, precipitation type (e.g., rain, snow, hail), and motion.

Demerits or Faults:

            i-       It has little coverage over oceans or remote regions

ii- It is Expensive to operate even for Developed Countries. 3-Satellite:

                                Although surface precipitation gauges are considered the standard for measuring precipitation, there are many areas in which their use is not feasible. This includes the vast expanses of ocean and remote land areas. As a result, the modern global record of precipitation largely depends on satellite observations. Satellites can give regular assessments of precipitation at a worldwide scale. 

i-Earth-observing satellites:

                             It can provide frequent estimates of precipitation at a global scale. These data are extremely useful for filling in data gaps that exist between rain gauge and ground-based radar sites and offer insights into when, where, and how much precipitation is falling worldwide. 

Demerits or Faults: I. Their disadvantage is measures cloud-top properties instead of rain, may mistake cirrus for rain clouds, does not capture rain from warm clouds. II. Satellite measures the value of precipitation which actually not occurs because it measures the precipitation value by wavelength and frequency. 4-Metrological Station:

                              A weather station is a facility, either on land or sea, with instruments and equipment for measuring atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include temperature, atmospheric pressure, humidity, wind speed, wind direction, and precipitation amount. Weather conditions out at sea are taken by ships and buoys, which measure slightly different meteorological quantities such as sea surface temperature (SST), wave height, and wave period. 

Demerits or Faults: I. They provide No coverage over oceans or remote regions. II. They are Point measurement not representative of area. III. Wind underestimates of rain.

Result:

                          I think Radar is the most reliable source of finding out the value of the precipitation because it measures precipitation on large area and also provide data of better spatial and temporal resolution. On the other hand, Metrological stations (Rain Gauges) having demerits in finding out the value of rainfall like disturbance of wind, material of pan etc. and satellite also measures cloud-top properties instead of rain, may mistake cirrus for rain clouds, does not capture rain from warm clouds. That’s why Radar is the best among these to find out the value of Precipitation.

References

Kozu, T., Kawanishi, [http://T.,%20Kuroiwa,%20H.,%20Kojima,%20M.,%20Oikawa,%20K.,%20Kumagai,%20H.,%20Okamoto,%20K.I.,%20Okumura,%20M.,%20Nakatsuka,%20H.%20and%20Nishikawa,%20K.,%202001.%20Development%20of%20precipitation%20radar%20onboard%20the%20Tropical%20Rainfall%20Measuring%20Mission%20(TRMM)%20satellite.%20IEEE%20transactions%20on%20geoscience%20a T., Kuroiwa, H., Kojima, M., Oikawa, K., Kumagai, H., Okamoto, K.I., Okumura, M., Nakatsuka, H. and Nishikawa, K., 2001. Development of precipitation radar onboard the Tropical Rainfall Measuring Mission (TRMM) satellite. IEEE transactions on geoscience and remote sensing, 39(1), pp.102-116.] Wilson, J.W. and Brandes, E.A., 1979. Radar measurement of rainfall—A summary. Bulletin of the American Meteorological Society, 60(9), pp.1048-1060. Germann, U., Galli, G., Boscacci, M. and Bolliger, M., 2006. Radar precipitation measurement in a mountainous region. Quarterly Journal of the Royal Meteorological Society: A journal of the atmospheric sciences, applied meteorology and physical oceanography, 132(618), pp.1669-1692. Fabry, F. and Zawadzki, I., 1995. Long-term radar observations of the melting layer of precipitation and their interpretation. Journal of the atmospheric sciences, 52(7), pp.838-851. Harrison, D.L., Driscoll, S.J. and Kitchen, M., 2000. Improving precipitation estimates from weather radar using quality control and correction techniques. Meteorological Applications, 7(2), pp.135-144.

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