Development of spectra and broadband cloud optical depth calibration constant at near- sea- level by using ground based spectrometer

Nur Hasinah Najiah Maizan , (2014) Development of spectra and broadband cloud optical depth calibration constant at near- sea- level by using ground based spectrometer. Universiti Malaysia Sabah. (Unpublished)

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Abstract

One of the requirements to predict earth climate change over a long time is by monitoring thin ice cloud microphysical properties such as cloud optical depth (COD) accurately. COD T, is measurement of cloud transparency and it depends on the cloud thickness of vertical depth and moisture density. Previously, Langley calibration method was widely used to calibrate ground based instrument, but this calibration method have to take place at high altitude for stable atmosphere. For long time COD monitoring purpose, this calibration method is not efficient in terms of accessibility and economic prospect. Therefore, the purpose of this study is to develop spectra COD calibration constant at near- sea- level by using Perez Du- Mortier model and selected wavelengths is 470nm, 500nm, and 550nm. Data collection for calibration constant development has been conducted on April and May 2012 from 0640 to 0830 with every 3 minute time interval. After all required data was obtained, filtration process is conducted using PDM to select only clear data to form Langley plot for each wavelengths in order to obtain calibration constant k. Measurement data for COD retrieval was conducted on February 2014 from 0900 to 1400 with every 10 minute time interval in 5 days. calibrated COD reading for these 5 days is obtained by applied calibration constant k, within COD algorithm and results for COD measurement for these 3 wavelength fall within 0.56 until 1.70. Validation process was conducted by comparing broadband COD values measured by spectrometer and pyranometer. Data collection for validation purpose was collected on February 2014 from 0900 to 1400 with every 10 minute time interval in 5 days for entire wavelength and using same method like spectra COD retrieval. Results show minimum and maximum reading for calibrated broadband COD measured by spectrometer is 0.61 and 1.67 respectively. Meanwhile, minimum and maximum reading for pyranometer is 0.36 and 1.68 respectively. Broadband COD reading between these two instruments has slightly differences but their reading still dose to spectra COD. It can be concluded that this proposed calibration method is feasible in calibrating ground instrument to measure cloud optical depth at low altitude because it gave a positive result as the reading for spectra and broadband COD after using calibrated instrument fall within the average scale for thin Ice cloud optical depth in tropical area which is below than 2 and this results is supported by previous research.

Item Type:Academic Exercise
Uncontrolled Keywords:cloud transparency, cloud thickness, vertical depth, moisture density, earth climate change, Langley calibration method
Subjects:Q Science > QC Physics
Divisions:FACULTY > Faculty of Science and Natural Resources
ID Code:14635
Deposited By:IR Admin
Deposited On:06 Jun 2017 11:17
Last Modified:06 Jun 2017 11:17

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