1. Sponsors: National Aeronautics and Space Administration (NASA) NASA Goddard Space Flight Center (GSFC) NASA Goddard Institute for Space Studies (GISS) NASA New York City Research Initiative (NYCRI) The City College of New York Contributors: Prof. Fred Moshary, Ph.D., Prof. Barry Gross, Ph.D., Tom Legbandt Peter Martens, High School Teacher Erhan Posluk, Undergraduate Lowell Brazin, High School Student Future Research Repair and install new machines in various locations. Continue to further analyze incoming data; attempt to identify specific aerosol properties such as size, type, and displacement of these aerosols. Apply other algorithms for data filtering, then compare to our method of Least Squares. Measuring Aerosol Optical Depth Through Use of a MFRSR References http://sky.ccny.cuny.edu/wc/ http://icp.giss.nasa.gov/education/urbanmaap/aerosols/ aerosols_train6.html http://earthobservatory.nasa.gov/Features/Aerosols/ http://patarnott.com/atms749/pdf/MFRSRdescription.pdf Abstract There is a growing concern that our planet’s climate is changing dramatically due to the aerosols in our atmosphere. Aerosols are small solid and liquid particles suspended in gas that can reflect sunlight and alter cloud formations. On a global scale, they can dramatically affect global warming while on a local scale, modify precipitation as well as having an adverse impact on health. To measure particles directly on a large scale is impossible so remote sensing techniques that measure the optical response to aerosols must be used. The most useful “proxy” for air-pollution is the attenuation of light through the atmosphere (i.e Aerosol Optical Depth). Our study focuses on evaluating the quality of air by measuring the Aerosol Optical Depth with a Multi-Filter Rotating Shadowband Radiometer (MFRSR). A MFRSR is an instrument that simultaneously measures direct, diffuse, and total irradiance at six different wavelengths (415, 500, 615, 673, 870, and 940 nm). By identifying the irradiance at the ground and the position of the sun in the sky (the zenith angle), we can calculate the Atmospheric Optical Depth using Langley Regression; then ultimately calculate the Aerosol Optical Depth by subtracting the Molecular Optical Depth. With a measurement of Aerosol Optical Depth (AOD), it’s possible to estimate aerosol properties including size, type, and amount of the aerosols in the atmosphere. For our study, we focused on the AOD levels for Lamont-Doherty. Materials - MFRSR Results Langley Regression Data Analysis Procedure MFRSR is short for Multi-Filtering Rotating Shadowband Radiometer. Stepping Motor, Shadow band, Detector.The MFRSR has three main parts: the Stepping Motor, Shadow band, and Detector. The apparatus is calibrated according to the latitude adjustment; the stepping motor’s angle with the horizontal must be equal to the latitude of the site of use. Simultaneously measures direct, diffuse, and total irradiance at six wavelengths (415, 500, 615, 672, 870, and 940 nm). The multiple wavelengths help detect different aerosol particles; each wavelength can be used to detect different size particles. In order to quantify the extinction of light as it passes through the atmosphere, the Langley Regression method was used. It states, if the path of a solar beam increases (thus increasing the number of particles it runs into), the amount of solar energy decreases, before reaching the surface. Therefore, irradiance at the surface is a function of the extraterrestrial irradiance (V o ) and some extinction factor (namely e -mτ ). By measuring the irradiance at the ground with the MFRSR and calculating the corresponding position of the sun (air mass), Beer’s law is applied the natural logarithm of each side is taken to draw a linear relationship between air mass and irradiance (left diagram). The slope of this linear relationship is the Total Atmospheric Optical Depth. Since the focus of the project is on aerosols, the Molecular Optical Depth is subtracted to obtain the Aerosol Optical Depth (AOD). Erhan Posluk, Lowell Brazin, Peter Martens Before beginning any data analysis, the data filtering technique (Least Squares Methods) requires that at least 60% of the data be usable (60% be a smooth curve). Clouds can have an adverse affect on the data and produce dips such as those seen below; these dips invalidate the data. V = Irradiance at ground Vo = Extraterrestrial Constant m = Air Mass τ = Aerosol Optical Depth After finding a day with reasonable data, a Matlab Program is created and used for the remaining computations. First the data is split into the morning and evening data according to solar noon. It is rare to find completely clear days, therefore the data must be filtered by first eliminating cloudy days and then finding the best fit line and the standard deviation of the remaining data. The line of best fit will be the line with the minimum sum of the residuals (errors) squared. The standard deviation is used to create a tolerance level for the data; if a data point is a certain distance from a line, it is eliminated. i.e.: If a data point is 3 standard deviations (or greater) away from a line, it can be eliminated. This is an iterative process; with each round the line of best fit and standard deviation is recalculated. Then this process is repeated while lowering out tolerance level until a sufficient line of best fit is found. The slope of this line will be the Total Optical Depth. The results of our data filtering are displayed below. Conclusion After analyzing our data, we were able to draw the following conclusions: There is a strong correlation between our data calculations and those provided via the YESDAS server. A consistent increase in AOD was found in the transition from AM to PM data. This increase however is not homogeneous over all wavelengths. The effect is stronger as the wavelength becomes longer. There was a great amount of fluctuation on a day-to-day basis. However there were no significant trends noticed across the three month period. With a decreasing wavelength, there is an increasing AOD, both in AM and PM data. This observation concurs with current theory that states that particles of any size most affect the absorption of shorter wavelengths.