Summary of our field trip to The City College of New York
Michaelangelo_Brown _Trip Report
TO: Professor Viviana Vladutescu
FROM: Michaelangelo Brown
DATE: May 06, 2015
SUBJECT: Field Trip to City College Atmospheric Research Lab
On April 30, 2015, Professor Viviana Vladutescue took her EET 3120 (Sensors and Instrumentation) class on a field trip, to visit the Atmospheric Research Lab at The City College of New York. The purpose of the trip was to expose us to equipments/sensors used to collect data about our atmosphere (radiation, humidity, pollution, temperature etc). Professor Vladutescue explained to us how equipments like the CIMEL Sun Photometer, Backscatter Lidar, MFSRS Shadow-band, and the Microwave Radiometer worked. We were also given the web-address for the Atmospheric Research lab at The City College, so we could look at data collected by the instruments listed above.
The Microwave Radiometer scans the skies above City College’s Grove School of engineering from horizon to horizon. This device can scan and produce vertical profiles from the surface to an altitude/distance of 10km [since the antenna that detects the microwaves ratates horizontally]. The data measured and collected by this instrument is: high resolution temperature, relative humidity, water vapor profiles, and low-resolution liquid profiles. The MSRSR measures energy emitted at sub-millimeter to centimeter wavelengths [microwaves] from clouds and water vapor in the atmosphere. To measure air temperature, humidity, and barometric pressure a Met Sensor and a rain sensor are included.
The CIMEL Sun Photometer on top of the Grove School of Engineering is number 237 in a vast network of CIMEL Sun Photometers; which collects and transmits data to NASA and PHOTONS every hour via geosynchronous satellite uplink from all over the world. When light waves past through a particle or molecule smaller than its wavelength; the electric field of the light wave acts on the charges within these particles/molecules and cause them to move at the same frequency. When they move at the same frequency as the light wave moving through them, they emit/ scatter the color of that light wave. The blue color of the sky and the yellow tone of the sun is the Rayleigh scattering of sunlight in the earth’s atmosphere. There are many different gas molecules in our atmosphere and they all scatter a portion of the beam of light from the sun differently. Take the oxygen in our air for example. The wavelengths at the ultra-violet region of the color spectrum are absorbed by oxygen. The blue color of the sky is a mixture of all the scattered colors, mainly blue and green, since the wavelength of yellow and red are hard to scatter. Now, the attenuation of the different wavelength [caused by absorption and scattering of light waves by aerosols, water vapor and gasses] is detected by the CIMEL Sun Photometer, and depending on which wavelengths are severely attenuated, we can determine what is in our atmosphere. To determine let say how much water vapor is in the air; scientist would pay close attention the wavelengths that are absorbed and scattered by water vapor. To determine aerosol optical depth scientist subtract the Total Optical Depth [ozone optical depth (OOP), Mixed Gas Optical Depth, Water Vapor Optical Depth]; from the suns photometer measurements.
L.I.D.A.R which stands for Light Detection And Ranging is similar to sonar and radar technology. This instrument takes advantage of Raman Scattering of light waves [not to be confused with the Rayleigh scattering]. The laser shot into the atmosphere will encounter particles in its line of sight. Now, Raman scattering says the object in the path of the laser will absorb and reflect photons from the laser. The reflected photon’s energy of the photon upon return to the LIDAR apparatus; will either be lower of higher than the original energy of the laser. The energy difference is caused by the energy required to excite the molecule of the object in the laser’s path to a higher vibration mode. The returning light can be used to develop 2D and 3D plots. Some applications for this process are:
- Aerosol Vertical Concentration (Backscatter Lidar)
- Water vapor concentration in the upper atmosphere (Raman Lidar)
- Cirrus Cloud Lidar
- Atmospheric component concentration (DIAL Lidar)
- Vertical mapping of buildings (Ranging Lidar)
CCNY Lidar System:
Output wave-lengths: 1064nm, 532nm, 386nm, and 355nm
Telescope: 20 inch Newtonian Reflector, F3.5
Detectors: APD (silicon enhanced avalanche photodiode), PMT (Hammamatsu Photomultiplier tubes)
Digitizing System: Lidar Transient Recorder TR 40-160 (LICEL) with 12 bit ADC [Analog to digital converter]
Because the laser emitted from the Lidar is so powerful, and because of Rayleigh scattering; a vertical radar emitter and antenna will search for aircrafts within the vicinity. If an aircraft is detected the laser beam is disabled and data collection is halted.
