week 03 - stats & RS

Question 1

why sample?

Answer 1

• saves time
• consistency of method
• expensive or impossible for complete enumeration
• partial knowledge is a normal state

Question 2

pops / params / estimates

Answer 2

• population: aggregate of unit values
• parameter: a constant used to characterize a particular population
• estimate: a value calculated from a sample in a way that makes it a “good” approx. to a parameter
• statistic: a value calculated from a sample

Question 3

variables (2)

Answer 3

1. continuous: a var that can be measured using numerical scale & subdivided infinitely
2. discrete:
   
   • attribute: binomial or multinomial
   • counts (# trees / acre)

Question 4

bias / accuracy / precision

Answer 4

• bias: systematic distortion
• accuracy: nearness to true (or pop.) value
• precision: clustering of unit values to their own mean

Question 5

distribution Fx

Answer 5

show for a sample (or pop) the relative freq w/ which different values occur

• of sexes: binomial / categorical (discrete)
• heights: continuous

Question 6

mu / xbar / s²_x / s_x

Answer 6

• Greek = parameters:
  
  • µ: population mean
  • σ²: population variance
• English = stats
  
  • xbar: sample mean
  • s²_x : sample variance
  • s_x: standard deviation

Question 7

subscripts can be either ___ or ___

Answer 7

• unit in a sample
• diff pops of values (x₁ = tree height; x₂ = DBH)

Question 8

covariance / correlation

Answer 8

• covariance: indicated association between two vars
  
  • positive: direct assoc
  • negative: indirect assoc
  • zero (or nearly): not assoc
  • can be related to magnitude of the unit values
• correlation:
  
  • unaffected by mag. of unit values
  • -1 to 1, and closer it is to either, stronger the assoc.

Question 9

normal distribution

Answer 9

• The distribution is bell-shaped; symmetrical about mean
• The mean locates the center of the distribution.
• The standard deviation is the distance b/t the mean and the inflection point of the distribution function.
• The distribution covers the entire real number line, from -∞ to +∞
• 2 parameters: the mean µ, and variance σ²

Question 10

stats summary

Answer 10

• Basic Concepts
  
  • Populations have parameters
  • Samples have statistics (to estimate parameters)
• Tools of the Trade
  
  • Standard deviation is the square-root of variance
  • Standard deviation (sd) and Standard Error (se) both quantify dispersion
    
    • SD for dispersion of sample values
    • SE for dispersion of sample mean values
• Normal distribution
  
  • The normal distribution has nice properties for describing a population of values measured on a continuous scale (number line)
  • The “Normal” does not do everything for us; we need to use the “t” distribution when pop’n variance is unknown and especially when we have small samples
• Also recall:
  
  • SRS: simple random sampling
    
    • CI: confidence interval
      
      • estimate +- 2(SE) or +- t(SE)

Question 11

remote sensing

Answer 11

the science and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring, and interpreting images and patterns of energy

Question 12

RS: passive/active

Answer 12

• passive: photographs; at NADIR alllows measurements
  
  • usually req’s source of energy (sunlight); has shadows
• active: LiDAR, illuminates objects with lasers
  
  • gathers height, intensity, and more

Question 13

topographical tools

Answer 13

• stereo aerial photography: used to make all topo maps
• photogrammetry: still stereo overlap, but now digital and using computers

Question 14

usable electromagnetic spectrum

Answer 14

• limited to visible & infrared
• some UV, but w/ atmospheric interference
• E_R = E_I - (E_T + E_A)
  
  • reflectance = incident - (transmitted + absorbed)

Question 15

vegetation index

Answer 15

• measurement of vegetative health
• steeper slope = healthier veg
  
  • because it’s absorbing so much red band that there isn’t as much reflected so the jump up to the infrared is large
• includes “soil line”, which can be used as baseline to compare different areas

Question 16

types of composites

Answer 16

• true color & false color
• bonus tip: GROUND TRUTHING