Archive for the 'College' Category

Radiometric terms/notes

General terms:

  • Emissivity ϵ(λ) – The ratio of the spectral exitance, Mλ(T), from an object at temperature T to the exitance from a blackbody at the same temperature MλBB(T) (unitless).

ϵ(λ)=(M_λ(T))/(M_λBB(T))

  • Absorptivity – The ability of the material to remove electromagnetic flux from the system by converting incident flux to another form of energy (e.g.) thermal energy. The absorptance α can be expressed as the ratio of the flux per unit area incident on the surface that is converted to another form of energy (Mα) to the irradiance on the surface.

α=M_α/E_i

  • Reflectivity – The ability if the material to turn incident flux back into the hemisphere above the material and the reflectance r can be expressed as the ratio of the exitance from the front of the sample (Mr) to the irradiance on the front of the sample.

r=M_r/E_i

  • Transmissivity – The ability of the material to allow the flux to propagate through it. The transmittance or transmission (τ) can be expressed as the unitless ratio of the exitance from the back of the sample (Mτ) to the irradiance on the front of the sample (Ei).

Hemispherical measurements:

  • Radiant flux density – The amount of radiant flux (or power) crossing a unit of area, and is measured in W m-2. Radiant flux density is also known as intensity or irradiance.
  • Irradiance (E) – The rate at which radiant flux is delivered to a surface (e.g. the responsive surface of a detector).

E=E(x,y)=dϕ/dA [Wm^(-2)]

  • Radiant exitance – The flux per unit area away from the surface (e.g. the power per unit area radiated by a source or reflected from a surface.

M=M(x,y)=dϕ/dA [Wm^(-2)]

  • Radiant spectral flux density – Flux per unit wavelength interval and designated with a wavelength subscript.
  • Spectral irradiance – Function of photon wavelength (or energy), denoted by F, is the most common way of characterising a light source. It gives the power density at a particular wavelength. The units of spectral irradiance are in Wm-2µm-1. The Wm-2 term is the power density at the wavelength λ(µm).
  • Spectral radiant exitance – Funtion of photon wavelength, flux of a particular wavelength per unit area away from the surface (e.g. the power per unit area radiated by a source or reflected from a surface.

Directional measurements:

  • Radiant intensity – Both the irradiance and exitance provide spatial information about the flux, but no angular or directional information. The simplest term used to describe directional or dispersive information about the flux is the radiant intensity (I):

I=I(θ,ϕ)=dϕ/dΩ [W〖sr〗^(-1)]

  • Radiance – Radiant intensity provides directional information, but not spatial information. Radiance (L [wm-2sr-1] overcomes this limitation. It is the most complicated of the radiometric terms, but also the most useful. It is defined in the equation below where x and y define a location in the plane of interest, and θ and ɸ are angles that define the direction of interest relative to the normal to the plane. The radiance is the flux per unit projected area (at the specified location of the plane of interest) per unit solid angle (in the direction specified relative to the reference plane).

L=L(x,y,θ,ϕ)=(d^2 ϕ)/dAcosθdΩ=dE/dΩcosθ=dI/dAcosθ=dM/dΩcosθ

  • Spectral radiance – The radiance of a surface per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength.
  • Solid-angle () – A two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large the object appears to an observer looking from that point. In the International System of Units (SI), a solid angle is expressed in a dimensionless unit called a steradian (symbol: sr).
  • Radiant energy – The energy of electromagnetic waves
  • Radiant flux – The rate of flow of energy (rays/photons passing), and is the first derivative of the radiant energy with respect to time (t):

ϕ=dQ/dt [Watts,W]

  • Radiation – The emission or transmission of energy in the form of waves or particles (photons) through space or through a material medium
  • Energy – Each photon carries energy dependent on the wavelength of photon:

q=hc/λ

  • Where:
    • h = Planck’s constant (6.6256*10-34 [joules*sec])
    • c = Speed of light (2.99792458*108 [m/s]
    • λ = wavelength

Weibull Distribution Confusion

There is a surprising number of conflicting definitions for Weibull Distribution PDF, specifically where the shape and scale parameters are swapped. I was working on an assignment for an engineering class and noticed that the formula that my professor provided was different from the formula in our book, where the α and β parameter values were swapped. In the end I followed my book and assumed that α was the shape parameter, and β the scale parameter. The list below illustrates some of the inconsistencies online that I stumbled across:

α = shape, β = scale

α = scale, β = shape

Seriously, WTF?

Live from Afghanistan it’s Saturday night

kankleIt has been a long time my friends. For that I apologize. I have been busier than a one legged man in an ass kicking contest. Actually, presently, I am a one legged man looking for an ass kicking contest. 10 Days ago I rolled my ankle again. It didn’t feel too bad this time compared to the situation I had in 2000. Somehow though I just found out that I may be out of sports and everything else I enjoy (Dancing With the Stars) until about Christmas. Honestly, I am a bit bummed by it but what’s a one legged guy gonna do?

Back to more important items. We had a sandstorm shortly after I wrote my last entry. That was kind of fun. I saw the dark gray clouds coming and thought that it was a typical rainstorm. As it got nearer I noticed that it was awfully dark and ominous looking for a simple rain shower. It began sprinkling and a couple of minutes later the sand came, and came, and came. I felt like one of those worms in Tremors. We got some good pictures of the event. Check my Afghanistan gallery in a couple of days for them. I am also going to upload a video that shows the clouds of sand flying over the mountains nearby. Pretty crazy stuff.

A couple of friends from Riley and I have randomly become popular here. I suppose we most of our friends through playing volleyball. It seems that we hang out or chew the fat with at least 5 people nightly. Last night we spent time with 17 different people in a couple of hours. It is kind of getting weird, but we feel like we know everyone on base. We are to this base what Tom is to MySpace. Where do we pick up our awesomeness medals?

One of the reasons why people may know us is because we have already begun brainstorming and even following through on crazy ideas, and stunts. For instance, Doty grabbed his wooden sword that was left to him (you have to see this thing in the Afghanistan gallery) and a wooden trash can lid, donned my volleyball helmet, and perched himself up on our roof to protect our hut from dragons one night. This went on for a while before somebody called the base police suggesting that some drunken dude in a medieval outfit was going to jump off the roof. The irony of that situation was that the cop that was dispatched was our friend who found the whole thing really funny. Doty then proceeded to burst into the cafeteria and eat some ice cream like that. The puzzled looks were priceless.

One of my closest friends just so happens to be a Special Friend. See my previous post for what that means. We have been spending a lot of time together, even though he is smitten by our local Lucy Lu physical therapist. It all started when he took Jared and I to their compound to show off all of their weapons and to show us the bullet riddled Humvees that were involved in the battle that claimed the lives of 10 French Soldiers. Again, for the two blog fans I have out there, the pictures will soon be posted in the Afghanistan Gallery. Unfortunately we are in a wonder years situation as many of our closer friends will be leaving to get out of here soon.

I finally had a suit made here. I cannot recall a better deal than a custom fitted quality pin striped suit modeled to look like an Armani, a custom fitted undershirt, and a tie for 65 dollars. Needless to say I am a very happy customer. Pictures will be posted soon. I plan on getting a couple more.
So it seems as though my military career is coming to an end soon. Only one year left. I have already begun thinking about jobs in central Texas. I am still kind of torn on that situation. No matter how much I love central Texas I still feel that I belong in a cold piney environment. That seems to be when I am most happy. I suppose I will just go with the flow and see where we all end up.

I just finished the last class of my Grad school. I cannot believe it actually happened. I have to admit it came and went so fast. I can honestly see myself pursuing another graduate degree and perhaps, eventually, a post grad degree. I am happy to have my own time now to explore and pursue the random things that I find myself exploring or pursuing.

Oh yes, one other side note, is actually a bit of a disappointment for me; we had an earthquake here a little over a week ago. It registered as a 5.9. I do not know how I did not feel it. I was walking to my office when it happened. I remember everyone in the shop looking around confused as I entered through the doorway. I heard “what the hell was that?” from a few people and by the time I realized what they were talking about the whole thing had come and gone. I might chalk that up to the helicopters that fly overhead and shake everything on base. Who knows? Somehow, someway I missed my first real earthquake.




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