1
00:00:02,250 --> 00:00:03,083
Hey, everybody.

2
00:00:03,083 --> 00:00:05,370
Welcome to Remote Sensing Foundations.

3
00:00:05,370 --> 00:00:07,650
This is the first lecture of the class,

4
00:00:07,650 --> 00:00:08,760
and I'm super excited

5
00:00:08,760 --> 00:00:12,270
to dive into remote sensing with you all.

6
00:00:12,270 --> 00:00:16,860
Remote sensing is a skill
that I learned in grad school

7
00:00:16,860 --> 00:00:20,710
and has sensed dictated
a lot of my research

8
00:00:22,230 --> 00:00:23,760
and professional career.

9
00:00:23,760 --> 00:00:26,160
It's super fun and super powerful,

10
00:00:26,160 --> 00:00:29,253
and I hope that at the end of this class,

11
00:00:30,630 --> 00:00:32,400
you too will be amazed

12
00:00:32,400 --> 00:00:35,430
at all the possibilities
of remote sensing.

13
00:00:35,430 --> 00:00:36,510
So in this first lecture,

14
00:00:36,510 --> 00:00:40,170
I'm gonna introduce you
to what remote sensing is,

15
00:00:40,170 --> 00:00:43,230
including explaining how
particle physics relates to it.

16
00:00:43,230 --> 00:00:44,550
I know that sounds a bit scary,

17
00:00:44,550 --> 00:00:46,980
but hopefully we'll break it down a bit

18
00:00:46,980 --> 00:00:48,363
so it's not so scary.

19
00:00:49,446 --> 00:00:50,700
Upon completion of this module,

20
00:00:50,700 --> 00:00:53,220
my hope is that you'll be
able to define remote sensing,

21
00:00:53,220 --> 00:00:55,653
define how and where it's used,

22
00:00:56,850 --> 00:00:58,110
name and define the components

23
00:00:58,110 --> 00:00:59,910
of the electromagnetic spectrum,

24
00:00:59,910 --> 00:01:03,420
and understand how energy
and matter interact

25
00:01:03,420 --> 00:01:05,253
with the surface terrain.

26
00:01:06,540 --> 00:01:10,500
Great, so let's get started.
What is remote sensing?

27
00:01:10,500 --> 00:01:12,210
Perhaps the most simplified definition

28
00:01:12,210 --> 00:01:16,920
would be the collection of
information about an object,

29
00:01:16,920 --> 00:01:19,920
but without making
physical contact with it.

30
00:01:19,920 --> 00:01:20,970
For the purpose of this course,

31
00:01:20,970 --> 00:01:23,820
I'm gonna add some words
to that definition.

32
00:01:23,820 --> 00:01:28,110
So I think of remote
sensing as the science

33
00:01:28,110 --> 00:01:31,530
of identifying, observing,
collecting, and measuring objects

34
00:01:31,530 --> 00:01:34,890
without coming into
direct contact with them,

35
00:01:34,890 --> 00:01:38,220
so without touching them,
without smelling them,

36
00:01:38,220 --> 00:01:39,483
without tasting them.

37
00:01:40,320 --> 00:01:42,660
I know usually we think of remote sensing

38
00:01:42,660 --> 00:01:45,330
just as a visual thing,

39
00:01:45,330 --> 00:01:50,330
but in terms of the
comprehensive definition of it,

40
00:01:50,340 --> 00:01:53,943
really all of the senses
can be remotely sensed.

41
00:01:54,930 --> 00:01:59,220
So in that sense, remote
sensing is carried out by humans

42
00:01:59,220 --> 00:02:03,720
and animals with the aid of
our eyes and other senses,

43
00:02:03,720 --> 00:02:06,720
like smell and hearing every day.

44
00:02:06,720 --> 00:02:09,480
Another important point that I
wanna make is that satellites

45
00:02:09,480 --> 00:02:13,020
don't actually take
pictures of our planet.

46
00:02:13,020 --> 00:02:16,650
Instead, what they do is
record electromagnetic energy

47
00:02:16,650 --> 00:02:20,460
that is reflected or omitted
from objects on Earth.

48
00:02:20,460 --> 00:02:23,550
And that point will become more clear

49
00:02:23,550 --> 00:02:25,743
in the next couple of slides.

50
00:02:28,500 --> 00:02:32,850
So before I jump into
how physics is related

51
00:02:32,850 --> 00:02:35,340
to remote sensing, I
just wanna demonstrate

52
00:02:35,340 --> 00:02:39,360
how broadly used remote sensing is.

53
00:02:39,360 --> 00:02:42,030
So I won't read this entire slide to you,

54
00:02:42,030 --> 00:02:44,070
but you can see that
remote sensing analysis

55
00:02:44,070 --> 00:02:45,900
is used in many sectors,

56
00:02:45,900 --> 00:02:49,380
and also where it is used
is growing each year,

57
00:02:49,380 --> 00:02:52,350
from commercial applications to non-profit

58
00:02:52,350 --> 00:02:54,750
to science, engineering, medicine.

59
00:02:54,750 --> 00:02:57,760
There's a whole host of
different career options

60
00:02:58,800 --> 00:03:01,830
for people who do remote sensing analysis.

61
00:03:01,830 --> 00:03:05,463
So it's not just an academic pursuit.

62
00:03:06,990 --> 00:03:10,203
It's used in a lot of different jobs.

63
00:03:11,280 --> 00:03:14,280
Okay, so let's now dive deeper
into some of the science

64
00:03:14,280 --> 00:03:17,583
behind what we are
measuring in remote sensing.

65
00:03:21,000 --> 00:03:23,190
Great, so now we're
gonna go back to physics

66
00:03:23,190 --> 00:03:24,870
to understand light or energy.

67
00:03:24,870 --> 00:03:26,640
And this may be background for some of you

68
00:03:26,640 --> 00:03:31,380
if you recently took physics
in college or high school.

69
00:03:31,380 --> 00:03:34,800
A photon is one of the
fundamental particles in physics

70
00:03:34,800 --> 00:03:36,513
and it's a light particle.

71
00:03:37,650 --> 00:03:41,190
By fundamental I mean
that it cannot be split,

72
00:03:41,190 --> 00:03:43,680
it doesn't have a substructure.

73
00:03:43,680 --> 00:03:45,270
And photons are really interesting

74
00:03:45,270 --> 00:03:49,200
because they exhibit a
wave particle duality.

75
00:03:49,200 --> 00:03:54,200
So in experiments when scientists
such as Albert Einstein

76
00:03:54,780 --> 00:03:58,680
were trying to figure
out whether photons were,

77
00:03:58,680 --> 00:04:01,473
or whether light behaved
as particle or waves,

78
00:04:02,460 --> 00:04:04,890
depending on the experiment

79
00:04:04,890 --> 00:04:08,880
and whether you were trying
to detect photons or not,

80
00:04:08,880 --> 00:04:11,640
the signal shows up as
a wave or a particle,

81
00:04:11,640 --> 00:04:13,920
so, very interesting.

82
00:04:13,920 --> 00:04:15,543
In its wave form,

83
00:04:17,310 --> 00:04:20,280
light, it can be seen as
electromagnetic waves,

84
00:04:20,280 --> 00:04:21,930
which is basically the combined movement

85
00:04:21,930 --> 00:04:25,110
of magnetic and electric fields.

86
00:04:25,110 --> 00:04:27,750
And these waves can be defined

87
00:04:27,750 --> 00:04:29,940
by their wavelength and frequency,

88
00:04:29,940 --> 00:04:34,290
and that determines how
much energy is emitted.

89
00:04:34,290 --> 00:04:36,600
I wanna make the point that frequency

90
00:04:36,600 --> 00:04:38,820
and wavelength are inversely related.

91
00:04:38,820 --> 00:04:43,620
So as frequency goes up,
wavelength goes down.

92
00:04:43,620 --> 00:04:48,360
As wavelength gets longer,
frequency gets shorter.

93
00:04:48,360 --> 00:04:51,720
So wavelength is basically the sort of,

94
00:04:51,720 --> 00:04:56,190
it's the width of your sine wave.

95
00:04:56,190 --> 00:04:59,880
And then the frequency
is the time that it takes

96
00:04:59,880 --> 00:05:03,183
for one wave oscillation to happen.

97
00:05:04,230 --> 00:05:07,650
You can see in the equations
at the bottom that frequency

98
00:05:07,650 --> 00:05:11,340
and wavelength are related
by the speed of light.

99
00:05:11,340 --> 00:05:15,330
So frequency is equal to the
speed of light over wavelength

100
00:05:15,330 --> 00:05:17,250
and the speed of light is a constant.

101
00:05:17,250 --> 00:05:19,770
And then if you're trying
to calculate energy,

102
00:05:19,770 --> 00:05:24,770
energy is equal to Planck's
constant times frequency.

103
00:05:24,960 --> 00:05:26,460
And so of course because frequency

104
00:05:26,460 --> 00:05:28,800
and wavelength are related,

105
00:05:28,800 --> 00:05:32,193
you could also calculate
energy by your wavelength.

106
00:05:34,470 --> 00:05:38,970
So the electromagnetic
spectrum is the entire range

107
00:05:38,970 --> 00:05:42,660
of electromagnetic radiation
or energy based off of

108
00:05:42,660 --> 00:05:46,260
all of the different
frequencies or wavelengths.

109
00:05:46,260 --> 00:05:50,310
So it's everything from
the shortest wavelength,

110
00:05:50,310 --> 00:05:53,490
which would be super high frequency,

111
00:05:53,490 --> 00:05:55,620
and that corresponds to high energy,

112
00:05:55,620 --> 00:05:58,290
all the way to a super long wavelength

113
00:05:58,290 --> 00:05:59,970
and a short frequency,

114
00:05:59,970 --> 00:06:03,873
which would correspond
to a low energy state.

115
00:06:07,830 --> 00:06:09,960
This figure shows some of
the most common sources

116
00:06:09,960 --> 00:06:12,390
of electromagnetic energy.

117
00:06:12,390 --> 00:06:15,526
As you can see, there's a
lot of different sources

118
00:06:15,526 --> 00:06:17,190
of electromagnetic energy

119
00:06:17,190 --> 00:06:19,830
that we come into contact
with every single day.

120
00:06:19,830 --> 00:06:24,270
And these have a variety of
wavelengths and frequencies.

121
00:06:24,270 --> 00:06:27,750
So on the left side of this
figure, you can see sources

122
00:06:27,750 --> 00:06:32,750
that have long wavelengths
and low frequencies,

123
00:06:33,180 --> 00:06:38,180
so such as subway systems,
AM/FM radios, cell phones.

124
00:06:42,317 --> 00:06:43,980
And then on the right side of this figure

125
00:06:43,980 --> 00:06:47,610
you can see sources that
have short wavelengths

126
00:06:47,610 --> 00:06:51,330
and high frequencies,
such as medical X-rays.

127
00:06:51,330 --> 00:06:53,043
In terms of this class,

128
00:06:54,300 --> 00:06:55,770
one of the most important sources

129
00:06:55,770 --> 00:07:00,330
of electromagnetic radiation
that we will study is the Sun.

130
00:07:00,330 --> 00:07:02,940
And I wanna point out
that there are a variety

131
00:07:02,940 --> 00:07:07,103
of different kinds of
radiation that the Sun emits.

132
00:07:08,160 --> 00:07:11,730
So we have the visible light,

133
00:07:11,730 --> 00:07:15,030
so red, green, blue light
that we can see with our eyes,

134
00:07:15,030 --> 00:07:17,010
but there's also radiation

135
00:07:17,010 --> 00:07:19,170
that we cannot see with
our eyes at the sentiment.

136
00:07:19,170 --> 00:07:24,170
So infrared or ultraviolet
radiation, again, we can't see,

137
00:07:25,200 --> 00:07:30,200
but can be very important
sources of radiation

138
00:07:30,270 --> 00:07:31,443
in remote sensing.

139
00:07:33,630 --> 00:07:35,400
All of the energy from the Sun

140
00:07:35,400 --> 00:07:39,090
that reaches the Earth is
called solar radiation.

141
00:07:39,090 --> 00:07:41,220
A very simplified view of remote sensing

142
00:07:41,220 --> 00:07:43,440
would be to say that remote sensing

143
00:07:43,440 --> 00:07:46,380
is measuring the reflection
of the Sun's radiation

144
00:07:46,380 --> 00:07:47,670
as it comes into contact

145
00:07:47,670 --> 00:07:49,713
with different surfaces on the Earth.

146
00:07:50,850 --> 00:07:54,090
However, solar radiation
does not take a straight path

147
00:07:54,090 --> 00:07:57,660
from the Sun to the Earth
and then back from the Earth

148
00:07:57,660 --> 00:08:00,753
to whatever sensor is trying
to measure that radiation.

149
00:08:01,680 --> 00:08:06,680
You can see in this graph that
around 6% of solar radiation

150
00:08:07,140 --> 00:08:09,450
is reflected by the atmosphere,

151
00:08:09,450 --> 00:08:12,720
16% is absorbed by the atmosphere,

152
00:08:12,720 --> 00:08:15,570
20% is reflected by the clouds,

153
00:08:15,570 --> 00:08:18,540
and 3% is absorbed by the clouds.

154
00:08:18,540 --> 00:08:22,470
Then when the remaining
radiation reaches the Earth,

155
00:08:22,470 --> 00:08:26,220
some of that energy or
radiation is absorbed

156
00:08:26,220 --> 00:08:29,880
into the Earth's surface
and some is reflected back.

157
00:08:29,880 --> 00:08:30,960
And then that radiation

158
00:08:30,960 --> 00:08:34,890
that's reflected back from
the Earth, it can be absorbed

159
00:08:34,890 --> 00:08:39,270
or scattered by the clouds
and the atmosphere as well.

160
00:08:39,270 --> 00:08:41,370
So spend a minute studying this graphic,

161
00:08:41,370 --> 00:08:44,880
and you can start to appreciate
how complex it can be

162
00:08:44,880 --> 00:08:48,840
to study and understand
the path light takes

163
00:08:48,840 --> 00:08:53,063
from the Sun to the Earth
and then back to a sensor

164
00:08:54,030 --> 00:08:57,573
that is trying to remotely
sense the Earth's surface.

165
00:09:01,470 --> 00:09:06,450
Here's another figure that
shows electromagnetic radiation

166
00:09:06,450 --> 00:09:09,510
going from the Sun to
the Earth to the sensor.

167
00:09:09,510 --> 00:09:11,580
I just wanted to add this figure

168
00:09:11,580 --> 00:09:15,810
because I think it shows
in a slightly different way

169
00:09:15,810 --> 00:09:18,690
all of the areas where
light can be scattered

170
00:09:18,690 --> 00:09:22,050
or absorbed, transmitted, emitted.

171
00:09:22,050 --> 00:09:24,120
Again, the important point here

172
00:09:24,120 --> 00:09:27,690
is that electromagnetic radiation
from the Sun is absorbed

173
00:09:27,690 --> 00:09:30,210
or scattered through the atmosphere

174
00:09:30,210 --> 00:09:33,633
both before and after it reaches Earth.

175
00:09:37,650 --> 00:09:40,890
Now, we'll jump into spectral signatures.

176
00:09:40,890 --> 00:09:44,340
Each surface on Earth, because
of its makeup and texture,

177
00:09:44,340 --> 00:09:47,310
has what is called a spectral signature.

178
00:09:47,310 --> 00:09:49,530
This basically is the unique distribution

179
00:09:49,530 --> 00:09:54,530
of reflected, emitted, and
absorbed radiation of an object.

180
00:09:54,540 --> 00:09:57,150
In this graph you can see
the percent reflectance

181
00:09:57,150 --> 00:09:59,460
of some common features
on the Earth's surface.

182
00:09:59,460 --> 00:10:03,840
So snow and ice are
very highly reflective,

183
00:10:03,840 --> 00:10:06,630
as well as clouds, whereas clear water

184
00:10:06,630 --> 00:10:10,560
and turbid water have very
low percent reflectance.

185
00:10:10,560 --> 00:10:12,450
You can also see that vegetation

186
00:10:12,450 --> 00:10:16,860
has a sort of unique spectral signature,

187
00:10:16,860 --> 00:10:18,363
and we'll talk about that,

188
00:10:19,740 --> 00:10:22,770
how that spectral signature
can help us identify them

189
00:10:22,770 --> 00:10:27,510
on the landscape on the following slide.

190
00:10:27,510 --> 00:10:28,650
You can also imagine

191
00:10:28,650 --> 00:10:30,900
that different satellites are constructed

192
00:10:30,900 --> 00:10:34,710
to measure different ranges
of spectral reflectance

193
00:10:34,710 --> 00:10:37,000
with high accuracy and precision

194
00:10:37,000 --> 00:10:41,190
in different wavelength ranges

195
00:10:41,190 --> 00:10:43,950
depending on what that satellite
is designed to measure.

196
00:10:43,950 --> 00:10:48,510
So for example, some
satellites are constructed

197
00:10:48,510 --> 00:10:51,390
to measure terrestrial surfaces,

198
00:10:51,390 --> 00:10:54,662
so they might be better
equipped to measure

199
00:10:54,662 --> 00:10:57,573
and differentiate between
different kinds of vegetation.

200
00:11:07,920 --> 00:11:09,870
So as I noted in the previous slide,

201
00:11:09,870 --> 00:11:14,870
vegetation can have very
unique spectral signatures,

202
00:11:14,970 --> 00:11:18,120
and that's really helpful
because it helps us differentiate

203
00:11:18,120 --> 00:11:20,370
between different kinds of vegetation,

204
00:11:20,370 --> 00:11:23,460
so for example, between
grasslands and forests.

205
00:11:23,460 --> 00:11:25,110
It can also help us differentiate

206
00:11:25,110 --> 00:11:28,710
between different plant species.

207
00:11:28,710 --> 00:11:32,160
But it can also help
us tell the difference

208
00:11:32,160 --> 00:11:36,420
between plants of the same
species that are healthy

209
00:11:36,420 --> 00:11:40,950
and unhealthy or that are
undergoing seasonal changes.

210
00:11:40,950 --> 00:11:44,010
So for example, in the
graph that I'm showing here,

211
00:11:44,010 --> 00:11:45,720
this is from a study that looked

212
00:11:45,720 --> 00:11:50,243
at leaves from the sweetgum
tree at different phases

213
00:11:51,120 --> 00:11:54,840
of going from green to brown

214
00:11:54,840 --> 00:11:58,170
and then falling off in the winter.

215
00:11:58,170 --> 00:12:00,570
And you can see that
the spectral signatures

216
00:12:00,570 --> 00:12:04,740
of these different colored
leaves are very, very different.

217
00:12:04,740 --> 00:12:09,740
And you can imagine that if
you had spectral information

218
00:12:10,364 --> 00:12:14,910
about these different leaves,

219
00:12:14,910 --> 00:12:19,910
you could learn to tell
from the light signatures,

220
00:12:21,150 --> 00:12:22,720
the spectral signatures

221
00:12:24,360 --> 00:12:28,680
which of these pixels
had more yellow leaves,

222
00:12:28,680 --> 00:12:30,420
which of them had more brown leaves,

223
00:12:30,420 --> 00:12:33,570
which of them had more green leaves.

224
00:12:33,570 --> 00:12:37,563
We'll explore this topic a
lot more in future lectures.