sensing and the environment

Question 1

What is a wave?

Answer 1

Field disturbances that transfer energy from one location to another

Question 2

What is a detector?

Answer 2

devices used to measure the characteristics of field disturbances

Question 3

What do characteristics of disturbances reveal?

Answer 3

information about a waves origin

Question 4

What can waves carry?

Answer 4

information from one location to another which is accessed by detection

Question 5

What can EM radiation tell us about stars?

Answer 5

material composition

Question 6

define passive sensing system

Answer 6

a system that generates a signal in response to a stimulus under normal environmental conditions
eg retina, some metal detectors

Question 7

Define an active detection system

Answer 7

a system where the sensor requires a non natural stimuli to generate a signal, eg x ray system, MRI

Question 8

Describe active detection in a cyber context

Answer 8

the sensor(s)uses a digital probe signal to instigate a response from a target, which is then measured. Requires more computing power and potentially less susceptible to data poisoning.

Question 9

Describe passive detection in a cyber context

Answer 9

the sensor(s) measure ambient digital signals only, without the use of a probe on the target. Can be more susceptible to data poisoning than active measures

Question 10

Describe binary classifiers

Answer 10

most detection cases we care about binary classification eg on/off, high/low, moving/stationary

in a security context - threat/non threat

Question 11

Describe a confusion matrix

Answer 11

red/green matrix, at simplest a 4 square grid

X axis - signal/actual/object
Y axis - detector response/predicted values

Green is real positives/negatives
Red is false positives/negatives

Question 12

What is the X axis of a confusion matrix?

Answer 12

X axis - signal/actual/object

Question 13

What is the Y axis of a confusion matrix?

Answer 13

Y axis - detector response/predicted values

Question 14

What are the green regions of a confusion matrix?

Answer 14

Green is real positives/negatives

Question 15

What are the red regions of a confusion matrix?

Answer 15

Red is false positives/negatives

Question 16

On a 4 square confusion matrix, what are the 4 binary classifiers?

Answer 16

True positive - TP
True negative - TN
False positive - FP
False negative - FN

Question 17

What are the 5 base calculations on a confusion matrix that help define how good a detector is?

Answer 17

Total positive = TP + FN
Total negative = FP + TN
Total true readings = TP + TN
Total false readings = FP + FN
Total readings = TP + TN + FP + FN

Question 18

how to calculate accuracy on a confusion matrix

Answer 18

Accuracy = total positive / total measurements

Question 19

What is specificity of a detector?

Answer 19

Specificity is the true positive rate

Question 20

How do you calculate specificity?

Answer 20

True positive rate = TP / (TP + FN)

Question 21

What is sensitivity of a detector?

Answer 21

true negative rate

Question 22

how do you calculate sensitivity?

Answer 22

true negative rate = TN / (FP + TN)

Question 23

What measure indicates that a detector will alarms correctly?

Answer 23

Specificity or true positive rate

Question 24

What gives the probability that a detector will alarm incorrectly?

Answer 24

Incorrect alarm rate = 1 - true negative rate

Question 25

Define a ROC curve?

Answer 25

Receiver Operator Characteristic curve

a way of plotting all possible confusion matrices to make it easy to identify the best threshold to make a decision.

Question 26

define the axis of a ROC graph

Answer 26

X - False positive rate (1 - sensitivity )
Y - true positive rate (specificity )

Question 27

What is 1, 1 on an ROC curve?

Answer 27

no true or false negatives

Question 28

What does going up the Y axis on the ROC curve mean?

Answer 28

increased probability of detection

Question 29

What does going up the x axis mean?

Answer 29

increase in the probability of false alarm

Question 30

What is AUC?

Answer 30

Area under the curve

Question 31

What is ROC sensitivity index?

Answer 31

d’ or D prime is the distance a ROC curve is from the 0,0 1,1 graph. in general, the further from the 0,0 1,1 grpah the better the sensor is, but this will be dependant on risk appetite for false alarms.