Analysis of Aerosol Particle Analysis of Aerosol Particle Concentration Using MFRSRConcentration Using MFRSR

Goddard Institute For Space Goddard Institute For Space StudiesStudies

The City College Of New York, The City College Of New York, Department of Electrical Department of Electrical

EngineeringEngineeringXavier EstevezXavier Estevez

What are aerosols?What are aerosols?

►Air consists of molecules of NAir consists of molecules of N22, O, O22, CO, CO22, , and various other gasesand various other gases

►Aerosols are fine solid or liquid Aerosols are fine solid or liquid particles suspended in a gasparticles suspended in a gas

►Some examples of atmospheric Some examples of atmospheric aerosols are smoke, sulfates, volcanic aerosols are smoke, sulfates, volcanic ash, pollen, mold sporesash, pollen, mold spores

Remote SensingRemote Sensing

• Is the observation of some attribute of a subject Is the observation of some attribute of a subject by means that do not involve direct contact by means that do not involve direct contact with that subjectwith that subject

• In other words, “look don’t touch”In other words, “look don’t touch”• A familiar remote sensing system is that of your A familiar remote sensing system is that of your

eyes and braineyes and brain• Examples of remote sensing: weather radar, Examples of remote sensing: weather radar,

satellite imagery, climbing a mountain and satellite imagery, climbing a mountain and looking at things, LIDAR, seismometers, looking at things, LIDAR, seismometers, telescopes, radio telescopes, x-rays, MRI. The telescopes, radio telescopes, x-rays, MRI. The applications are almost endless.applications are almost endless.

Remote Sensing of AerosolsRemote Sensing of Aerosols► In order to determine the In order to determine the

concentration of aerosols in concentration of aerosols in the atmosphere, we use the atmosphere, we use optical remote sensing.optical remote sensing.

► Aerosol particles reflect Aerosol particles reflect light. We can detect these light. We can detect these particles by measuring the particles by measuring the loss of intensity of light as it loss of intensity of light as it passes through an aerosol-passes through an aerosol-bearing mediumbearing medium

► Different wavelengths of Different wavelengths of light can detect different light can detect different particle sizes.particle sizes.

► Simply put, short Simply put, short wavelength light detects wavelength light detects smaller particles, and long smaller particles, and long wavelength light detects wavelength light detects larger particleslarger particles

Long wavelength light

Short wavelength light

ApparatusApparatus Multi-Filter Rotating Shadowband RadiometerMulti-Filter Rotating Shadowband Radiometer

Multi-FilterMulti-Filter►Senses several different wavelengths of lightSenses several different wavelengths of light

Rotating ShadowbandRotating Shadowband►Has a motorized arm thatHas a motorized arm that

periodically covers the periodically covers the sensorsensor

RadiometerRadiometer►Measures intensity of Measures intensity of

solar radiationsolar radiation

http://www.yesinc.com/products/data/mfr7/index.html

What Does It Tell Us?What Does It Tell Us?

The moving shadowband allows one The moving shadowband allows one instrument to collect direct and diffuse instrument to collect direct and diffuse intensity readingsintensity readings

Data analysis tells us how much light is Data analysis tells us how much light is reflected by the atmospherereflected by the atmosphere

Variations in this amount are related to Variations in this amount are related to concentration of aerosol particlesconcentration of aerosol particles

MethodsMethods

Control Unit /Data Acquisition

System

•Data Acquisition System (DAS) controls the MFR, stores data in internal memory

•Laptop is connected to the DAS to download the data

•Data files are analyzed using various software tools

RS-232

LaptopMFR

Program Flow Chart Program Flow Chart (simplified)(simplified)

File Splitter

Raw input data(23 columns, with outliers)

Separate files for each morning and afternoon

(7 columns, strippedof outliers)

Day Processor

2-DimensionalData Array Object

Values converted toSecant and log

Line FitterResults

List of optical depthsFor each of 5

different wavelengthchannels

Beer’s LawBeer’s LawThe deeper the glass, the darker the brew,The deeper the glass, the darker the brew,

The less the amount of light that gets throughThe less the amount of light that gets through

Ig = I0 e–m

Loge Ig = Loge I0 – m

•The intensity of the light that reaches the earth’s surface is decreased by two factors– the length of its path through the atmosphere, and the optical properties of the atmosphere

•The relationship can be modeled as a linear equation.

•The slope of this line is equal to the total optical depth (how effectively the atmosphere blocks light)

Ig = intensity of sunlight as measured at the instrument

I0 = intensity of sunlight outside of the atmosphere

e = Napier’s constant

m = airmass factor

= optical depth

Langley Regression AnalysisLangley Regression Analysis

► As the sun moves across the sky, sunlight must As the sun moves across the sky, sunlight must pass through varying amounts of airpass through varying amounts of air

► The light’s path is shortest at noon, and longest at The light’s path is shortest at noon, and longest at sunrise and sunsetsunrise and sunset

► Beer’s law tells us that there is a direct relationship Beer’s law tells us that there is a direct relationship between path length and light intensity– light that between path length and light intensity– light that passes through a path twice as long is affected passes through a path twice as long is affected twice as much.twice as much.

► We assume that the optical depth of the We assume that the optical depth of the atmosphere remains constant over a half-day atmosphere remains constant over a half-day period, and can therefore determine optical depth period, and can therefore determine optical depth by plotting light intensity against path length (the by plotting light intensity against path length (the secant of the solar zenith angle).secant of the solar zenith angle).

Data FilteringData FilteringThe optical depth for the time period in this graph is equal to the slope of the red line.

The red line was not drawn mathematically, it “just looks right”

This technique is not statistically valid, we have to use a linear regression equation to draw the trend line

That regression applied to this data set would yield a line with a less severe slope and a lower y-intercept, due to the disproportionate effect of outlying points.

Secant of solar zenith angle vs. log e Solar radiation intensity (W/m2/nm)

415 nm, afternoon of 22-June-2004

Linear RegressionLinear Regression

► Linear regression is a technique used to plot a straight line from a 2-Linear regression is a technique used to plot a straight line from a 2-dimensional collection of plotted data pointsdimensional collection of plotted data points

► This allows one to model real-world data theoreticallyThis allows one to model real-world data theoretically► The line produced will pass as closely as possible to as many of the The line produced will pass as closely as possible to as many of the

data points as possibledata points as possible► The equation which returns the slope of the best-fit line is as follows:The equation which returns the slope of the best-fit line is as follows:

ResultsResults

►The final product of my research is a The final product of my research is a list of optical depths for approximately list of optical depths for approximately 70 days, and the Java application that I 70 days, and the Java application that I used to calculate these values.used to calculate these values.

► I do not see any discernible patterns in I do not see any discernible patterns in these optical depths. They do not these optical depths. They do not appear to conform to any linear or appear to conform to any linear or periodic functions as far as I can tell.periodic functions as far as I can tell.

DiscussionDiscussion

► One potential source of error is the fact that One potential source of error is the fact that due to cloudy or overcast conditions, some due to cloudy or overcast conditions, some days did not yield any acceptable data-points, days did not yield any acceptable data-points, or yielded too few data-points to obtain any or yielded too few data-points to obtain any statistically valid trendstatistically valid trend

► Another error source is the fact that even the Another error source is the fact that even the best data-cleaning algorithm cannot best data-cleaning algorithm cannot determine with absolute certainty which determine with absolute certainty which readings are invalid.readings are invalid.

► This does not confirm or deny the validity of This does not confirm or deny the validity of the results. Further evaluation of the data is the results. Further evaluation of the data is needed in order to determine the value needed in order to determine the value

ReferencesReferences

► ““Atmospheric Aerosols: What are they, and why are they so Atmospheric Aerosols: What are they, and why are they so important?” important?” http://oea.larc.nasa.gov/PAIS/Aerosols.htmlhttp://oea.larc.nasa.gov/PAIS/Aerosols.html

► ““Linear Regression”Linear Regression”http://www.math.csusb.edu/faculty/stanton/probstat/regression.htmhttp://www.math.csusb.edu/faculty/stanton/probstat/regression.htmll

► ““Excel Tutorial On Linear Regression”Excel Tutorial On Linear Regression”http://phoenix.phys.clemson.edu/tutorials/excel/regression.htmlhttp://phoenix.phys.clemson.edu/tutorials/excel/regression.html

► ““Langley Method”Langley Method”http://www.optics.arizona.edu/rsg/menu_items/resources/equip/langley.htmhttp://www.optics.arizona.edu/rsg/menu_items/resources/equip/langley.htm

► “MFR-7 MULTI-FILTER ROTATING SHADOW BAND RADIOMETERMFR-7 MULTI-FILTER ROTATING SHADOW BAND RADIOMETER”

http://www.yesinc.com/products/data/mfr7/index.htmlhttp://www.yesinc.com/products/data/mfr7/index.html