Radiometers
Introduction to Radiometers
Agenda
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•
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How a radiometer works
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
2
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Radiometer Basics
Experimental Results
What is a radiometer?
A radio receiver that measures the average power of the noise coming in
within a certain range of frequencies (i.e. bandwidth).
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
3
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Radiometer system
Experimental Results
Radiometers are highly sensitive receivers designed to measure thermal
electronic emission by material media
--Microwave Remote Sensing
Fawwaz T. Ulaby
Richard K. Moore
Adrian K. Fung
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
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Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Radiometer system
Experimental Results
The primary goal of a radiometer is to measure power. While that
statement sounds easy, there are in fact many factors that go in to how
well a radiometer can measure the power it sees. A better statement
would be that a radiometer's primary goal is to accurately measure power
within a certain degree of accuracy. In order to accurately and within a
high degree of precision measure power, a radiometer must take into
account various factors such as the system noise, the bandwidth of the
signal and the stability of the system as a whole.
--Matthew E. Nelson
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
5
Equivalent Noise Temperature
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Everything is always moving
o electrons in a conductor are always in a state of random motion
o The kinetic energy of an electron is proportional to the physical temperature T
of the conductor
o This was explored by John Johnson and Harry Nyquist
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
6
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
About the thesis
Experimental Results
We can use this property to measure things remotely such as Soil
Moisture, Ocean Salinity and celestial bodies.
Soil Moisture and Ocean
Salinity (SMOS) satellite
Image courtesy of ESA
Matthew E. Nelson
::
Iowa State University
NRAO VLA
Image courtesy of NRAO/AUI
MTREO/AGRON/E E 518 ::
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SDR and Radiometer Basics
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
There are six stages common to all radiometers:
1.
2.
3.
4.
5.
6.
Source
Bandwidth
Amplification
Power detection
Data smoothing
Output
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
8
SDR and Radiometer Basics
System Noise
• Every device adds noise, even passive devices
• The higher the system noise, the lower the sensitivity
• The system noise masks the noise of our target
Matthew E. Nelson
::
Iowa State University
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
𝑁𝐸Δ𝑇 = Experimental Results
𝑇' + 𝑇)*)
𝜏 ∗𝛽
MTREO/AGRON/E E 518 ::
9
SDR and Radiometer Basics
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Power measurement
The key to the performance of a radiometer is to minimize noise generated internally
while amplifying the noise generated from the source.
• All components generate additional noise
• Low Noise Amplifiers (LNAs) are the largest contributors
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
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SDR and Radiometer Basics
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Radiometer Stability
Control Stability by maintaining physical
temperature
Compensate for instability
• Dicke Radiometer
• Correlating Radiometer
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
11
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
About the thesis
Experimental Results
Over the years, different types of radiometers have been developed.
Analog Radiometers
Digital Radiometers
Analog Front End
Hybrid
• LNAs and filters
• Square-Law detector
• A mix of analog and digital components
• Often digitizes after power detection
Direct Sampling
• Samples directly at the frequency of interest
• Uses digital signal processing to extract power
information
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
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Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
About the thesis
Experimental Results
The ISU Radiometer is a Direct Sampling Radiometer. It uses an analog
RF front end, but then samples (undersamples) the RF signal. It is also
a correlating radiometer.
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
13
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
About the thesis
Experimental Results
My research focused on improving this radiometer and using a software
defined radio to replace the direct sampling unit.
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
14
SDR and Radiometer Basics
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
A software defined radio is a device that digitizes a received RF signal as soon as possible, and processes
the digital representation of the signal using digital signal processing
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
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SDR and Radiometer Basics
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Hardware Platform
Dual 14-bit
ADC
25 MHz
bandwidth per
channel
Modular
daughterboard system
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
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SDR and Radiometer Basics
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
GNURadio and GNURadio Companion
GNURadio
GNURadio
Companion
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Open Source
Fast and Flexible
Python/C++
Excellent hardware support
• Drag and Drop
• Rapid GUI development
• Easy to expand
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
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SDR-Based Radiometer Implementation
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Implementation of a Software Defined Radio Based Radiometer
• Bandwidth 20 MHz
Hardware
• 1400 - 1420 MHz
Requirements • 𝑁𝐸Δ𝑇 = 1𝐾
• Easy to use GUI
interface for
Software
Requirements technician to use
• Easy to modify
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
18
SDR-Based Radiometer Implementation
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Mapping traditional radiometer to SDR-Based Radiometer – Power Detection
Analog
SDR
• Diode operating in
the Square-Law
region
Matthew E. Nelson
::
Iowa State University
• Square the
magnitudes
MTREO/AGRON/E E 518 ::
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SDR-Based Radiometer Implementation
Mapping traditional radiometer to SDR-Based
Radiometer – Data Smoothing
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
𝑦 𝑛 = 𝑎 4 ∗ 𝑥 𝑛 + 𝑏7 ∗ 𝑦[𝑛 − 1]
𝑦; =
Analog
𝑇
𝑅𝐶
𝑥; +
𝑦
𝑇 + 𝑅𝐶
𝑇 + 𝑅𝐶 ;>7
SDR
• Integrator a.k.a.
Low Pass Filter
Matthew E. Nelson
Experimental Results
::
Iowa State University
• Infinite Impulse
Response Filter
MTREO/AGRON/E E 518 ::
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SDR-Based Radiometer Implementation
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
SDR-Based Radiometer Graphical User Interface
Hardware
Control
Data
Display
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•
•
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Center Frequency
Bandwidth
Integration time
Filtering
• Raw total power
• Calibrated noise
temperature
• Spectrum
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
21
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Experimental Results
Experiment 1 – SDR-Based Radiometer Verification and Calibration
Setup
1.
2.
3.
4.
5.
N200 SDR
ADL5902 - Square-law detector
Power Divider
Traditional Radiometer RF Front End
Matched Load
Data Collection
• GNURadio
• Labview with ADC
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
22
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Experimental Results
Experiment 1 – SDR-Based Radiometer Verification and Calibration
Results
Successfully calibrated both the square-law detector and the SDR-Based Radiometer. The square-law
and SDR-Based Radiometer agree within .002 Kelvin
Square-law Detector
Matthew E. Nelson
::
Iowa State University
Square-law and SDR-Based Radiometer
SDR-Based Radiometer
MTREO/AGRON/E E 518 ::
23
Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Experimental Results
To verify our results, we can look at the Standard Deviation to determine if the radiometer is performing
as well as it should.
Sensitivity
Stability
• Expected - .1 Kelvin
• Measured - .23 Kelvin
Matthew E. Nelson
::
• Stayed within ~ +/- .15 Kelvin
over 15 min. period
Iowa State University
MTREO/AGRON/E E 518 ::
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Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Experimental Results
Experimental Results
Because we have most of radio defined in software, we can easily change the behavior by uploading new
software. An example of this the ability to detect and filter out an offending signal.
Total power measurements made
Interfering signal identified
Matthew E. Nelson
Offending signal filtered
::
Iowa State University
• SDR-Based Radiometer
• Analog Square-Law
MTREO/AGRON/E E 518 ::
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Radiometer Basics
ISU Radiometer
SDR-Based Radiometer
Example Usage Scenario
Experimental Results
Application Scenario: Soil Moisture reading with interfering signal
A radiometer is deployed Data is recorded with the
SDR-based radiometer.
in a field to take soil
Both total power and the I
moisture readings
and Q data is saved
Matthew E. Nelson
::
Iowa State University
If the radiometer is calibrated we
can now show a relationship
between the amount of power
received and the amount of soil
moisture
MTREO/AGRON/E E 518 ::
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For Today
Questions?
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
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Introduction
Related Works
Background
Implementation
Extra Slides
Experimental Results
Example Usage Scenario
Closing
Equations - Radiometer
𝑃 = 𝑘 ∗ 𝛽 ∗ 𝐺 ∗ (𝑇' + 𝑇C )
𝐹 = 𝐹7 +
𝐹J − 1 𝐹K − 1
𝐹L − 1
𝐹; − 1
+
+
+⋯+
𝐺7
𝐺7 𝐺J
𝐺7 𝐺J 𝐺K
𝐺7 𝐺J 𝐺K … 𝐺;
Δ𝑇O = 𝑇)*)
Δ𝐺
𝐺
Matthew E. Nelson
𝑁𝐹 = 10 ∗ log74 𝐹
𝑁𝐸Δ𝑇 = 𝑇' + 𝑇)*)
𝜏 ∗𝛽
𝑉QRS = 𝑛𝑉T;J = 𝑛𝑃T;
::
Iowa State University
MTREO/AGRON/E E 518 ::
28
Introduction
Related Works
Background
Implementation
Extra Slides
Filtering
𝑦 𝑛 = 𝑎 4 ∗ 𝑥 𝑛 + 𝑏7 ∗ 𝑦[𝑛 − 1]
𝑇 = 𝑇𝑖𝑚𝑒𝐵𝑒𝑡𝑤𝑒𝑒𝑛𝑆𝑎𝑚𝑝𝑙𝑒𝑠 =
𝑅𝐶
𝑏7 =
𝑇 + 𝑅𝐶
𝑦; =
𝑁𝐸ΔT =
::
Iowa State University
1
𝑓)
𝑇
𝑅𝐶
𝑥; +
𝑦
𝑇 + 𝑅𝐶
𝑇 + 𝑅𝐶 ;>7
𝑇' + 𝑇C
𝛽 − 𝛽eTfSgh 𝜏
Matthew E. Nelson
𝑉T; − 𝑉QRS
𝑑𝑉QRS
=𝐶
𝑅
𝑑𝑡
𝑥 ; − 𝑦;
𝑦; − 𝑦;>7
=𝐶
𝑅
𝑇
𝑎 4 = 1 − 𝑏7
𝑇
𝑎4 =
𝑇 + 𝑅𝐶
Experimental Results
Example Usage Scenario
Closing
𝑓a =
1
2𝜋𝑅𝐶
MTREO/AGRON/E E 518 ::
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Introduction
Related Works
Background
Implementation
Extra Slides
Experimental Results
Example Usage Scenario
Closing
Filter Fluctuations
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
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Introduction
Related Works
Background
Implementation
Extra Slides
Experimental Results
Example Usage Scenario
Closing
Difference between X2 and SDR
In LN2 ~ .0003 Kelvin. | In Ice, ~ .002 Kelvin
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
31
Introduction
Related Works
Background
Implementation
Extra Slides
Experimental Results
Example Usage Scenario
Closing
Difference between X2 and SDR
In LN2 ~ .0003 Kelvin. | In Ice, ~ .002 Kelvin
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
32
Introduction
Related Works
Background
Implementation
Extra Slides
Experimental Results
Example Usage Scenario
Closing
GUI Interface Full
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
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Introduction
Related Works
Background
Implementation
Extra Slides
Experimental Results
Example Usage Scenario
Closing
TPR Blocks in GNURadio
Power Detection
Matthew E. Nelson
::
Iowa State University
Integration
Low Pass Filter
MTREO/AGRON/E E 518 ::
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Introduction
Related Works
Background
Implementation
Extra Slides
Experimental Results
Example Usage Scenario
Closing
Soil Moisture Application
Matthew E. Nelson
::
Iowa State University
MTREO/AGRON/E E 518 ::
35