Cmplt Seminar Report - Copy

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Lunar Reconnaissance Orbiter Miniature RF Technology Demonstration

ABSTRACT

The Miniature Radio Frequency (Mini-RF) system is manifested on the

Lunar Reconnaissance Orbiter (LRO) as a technology demonstration and an extended

mission science instrument. Mini-RF represents a significant step forward in space borne

RF technology and architecture. It combines synthetic aperture radar (SAR) at two

wavelengths (S-band and X-band) and two resolutions (150 m and 30 m) with

interferometric and communications functionality in one lightweight (16 kg) package.

Previous radar observations (Earth-based, and one bistatic data set from Clementine) of the

permanently shadowed regions of the lunar poles seem to indicate areas of high circular

polarization ratio (CPR) consistent with volume scattering from volatile deposits (e.g.

water ice) buried at shallow (0.1-1 m) depth, but only at unfavorable viewing geometries,

and with inconclusive results. The LRO Mini-RF utilizes new wideband hybrid

polarization architecture to measure the Stokes parameters of the reflected signal. These

data will help to differentiate “true” volumetric ice reflections from “false” returns due to

angular surface regolith. Additional lunar science investigations (e.g. pyroclastic deposit

characterization) will also be attempted during the LRO extended mission. LRO’s lunar

operations will be contemporaneous with India’s Chandrayaan-1, which carries the

Forerunner Mini-SAR (S-band wavelength and 150-m resolution), and bistatic radar (S-

Band) measurements may be possible. On orbit calibration, procedures for LRO Mini-RF

have been validated using Chandrayaan 1 and ground-based facilities (Arecibo and

Greenbank Radio Observatories).

TABLE OF CONTENTS

Al Ameen engg.college Dept. of E.C.E

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CHAPTER NO. TITLE PAGE NO

ABSTRACT iv

LIST OF FIGURES vi

LIST OF TABLES vii LIST OF ABBREVIATIONS viii

1. INTRODUCTION 1

2. Why we require Mini RF technology 2

3. What is Mini RF Technology 3

4. Comparison of Mini RF Technology

With other Radar Systems 4

5. Mini-RF Instrument Description 5

5.1Hybrid-polarity architecture 7

5.2 Antenna 10

5.3 Transmitter 11

5.4 Interconnect Module 14

5.5 Receiver 14

5.6 Control Processor 14

6. Calibration 15

7. Data analysis and Interpretation 16

8. Stokes Parameters as clear evidence of lunar ice 18

9. Applications 19

10. Conclusion 20

11. References 21


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LIST OF FIGURES

FIGURE NO. NAME PAGE NO

1 Dual scattering caused by ice or roughness 2

2 LRO Mini-RF system functional block diagram 6

3 Hybrid-polarity architecture 7

4 Mini-RF antenna design 10

5 Mini-RF transmitter block diagram 12

6 Mini-RF Microwave Power Module

Traveling Wave Tube (MPM/TWT) 13

7 Mini-RF calibration strategy 17


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LIST OF TABLES

TABLE NO NAME PAGE NO

1 Radar System Comparisons with

Mini RF Technology 4

2 Communications System Comparison with

Mini RF Technology 4

3 Significant and Derivative of stock parameters 18


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LIST OF ABBREVIATIONS

LRO Mini-RF- Lunar Reconnaissance Orbiter Miniature Radio Frequency

NASA- National aeronautics and space administration.

CPR- High Circular Polarization Ratio

SAR- Synthetic Aperture Radar

MPM- Microwave Power Module

FPGA - Field Programmable Gate Array

OC- Opposite Sense

SC- Same Sense

TWT - Traveling Wave Tube

IM- Interconnect Module

QDWS- Quadrature Digital Waveform Synthesizer

ART - Arecibo Radio Telescope

GBT - The Green Bank (Radio) Telescope

POC- Payload Operations Center

PRF- Pulse Repetition Frequency

UAV- Unmanned Airborne Vehicles


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Chapter 1

Introduction

The Miniature Radio Frequency (Mini-RF) system is manifested on the Lunar

Reconnaissance Orbiter (LRO) as a technology demonstration and an extended

mission science instrument. Mini-RF represents a significant step forward in space

borne RF technology and architecture. It combines synthetic aperture radar (SAR) at

two wavelengths (S-band and X-band) and two resolutions (150 m and 30 m) with

interferometric and communications functionality in one lightweight (16 kg) package.

Previous radar observations (Earth-based, and one bistatic data set from Clementine)

of the permanently shadowed regions of the lunar poles seem to indicate areas of high

circular polarization ratio (CPR) consistent with volume scattering from volatile

deposits (e.g. water ice) buried at shallow (0.1–1 m) depth, but only at unfavorable

viewing geometries, and with inconclusive results. The LRO Mini-RF utilizes new

wideband hybrid polarization architecture to measure the Stokes parameters of the

reflected signal. These data will help to differentiate “true” volumetric ice reflections

from “false” returns due to angular surface regolith. Additional lunar science

investigations (e.g. pyroclastic deposit characterization) will also be attempted during

the LRO extended mission. LRO’s lunar operations will be contemporaneous with

India’s Chandrayaan-1, which carries the Forerunner Mini-SAR (S-band wavelength

and 150-m resolution), and bistatic radar (S-Band) measurements may be possible.

Data quality and instrument characteristics suggest that hybrid polarity is highly

desirable for future exploratory radar missions in the Solar system. The new

technologies being qualified on LRO Mini- RF include: Microwave Power Module

(MPM) based multi-frequency transmitter, wideband dual-frequency panel antenna, all

digital receiver and waveform synthesizer incorporating field programmable gate array

(FPGA) and analog-to-digital conversion at 1 GHz sampling. The Mini-RF parts

qualification program, which included commercial technology, allowed innovative

components to gain space qualification.


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Chapter 2

Why we require Mini RF technology

The LRO Mini-RF payload will address key science questions during the LRO

primary and extended missions. These include exploring the permanently shadowed

Polar Regions and probing the lunar regolith in other areas of scientific interest. The

nature and distribution of the permanently shadowed polar terrain of the Moon has

been the subject of considerable controversy. Previous earth based observations uses

that when an incident circularly polarized radar wave is backscattered off an interface,

the polarization state of the wave changes. For most surfaces, this leads to a return

with more of an “opposite sense” (OC) polarization than a “same sense” (SC)

polarization, so the circular polarization ratio (CPR=SC/OC) remains less than 1.

However, in weakly absorbing media (such as water ice) the radar signal can undergo

a series of forward scattering events off small imperfections in the material, each of

which preserves the polarization properties of the signal . Those portions of the wave

front that are scattered along the same path but in opposite directions combine

coherently to produce an increase in the SC radar backscatter .This coherent

backscatter effect leads to large returns in the same sense (SC) polarization and values

for CPR that can exceed unity. Note that CPR > 1, while diagnostic of water ice, is not

a unique signature for water ice. Very rough, dry surfaces have also been observed to

have CPRs that exceed unity. The CPR may increase in such regions due to double‐bounce scattering between the surface and rock faces. In order distinguish between

true ice and false ice mini RF technology will be helpful.

Figure .1 Dual scattering caused by ice or roughness


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Chapter 3

What is Mini RF Technology

The Mini-RF architecture is new. The hybrid-polarity design (transmitting circular

polarization and receiving coherently two orthogonal linear polarizations) provides

data sufficient to measure the 2 × 2 covariance matrix of the backscattered field, which

in turn lead to the four Stokes parameters. Analysis of these data, either by standard

radar astronomy methods or by applying matrix decomposition techniques, extracts all

information available in the radar reflections, thus providing a sharper tool than CPR

alone to help differentiate between “true” (ice) and “false” (regolith blockiness) lunar

returns. Mini-RF can operate as a dual-frequency, hybrid-polarity imaging radar

designed to collect information about the scattering properties of the permanently dark

areas near the lunar poles at optimum viewing geometry. As the LRO Mini-RF system

probes the lunar regolith at two frequencies (S-band and X-band) it will provide

additional information on the physical properties of the upper meter or two of lunar

surface. Under the proposed observational constraints, Mini-RF can identify areas of

high CPR (∼1), which could be caused by ice deposits. Areas that do show high CPR

can be analyzed with greater sensitivity through their backscattering features. It is

hypothesized that “ice” and “regolith” will have differentiable characteristics as seen

through their respective Stokes parameters at two wavelengths. When supported by

Chandrayaan-1 and other LRO data (e.g. neutron spectroscopy, shadow and lighting,

roughness and surface texture, thermal environment), the LRO Mini-RF measurements

should provide more conclusive evidence as to the likelihood that ice deposits occur in

permanently shadowed areas. Mini RF technology will be also be helpful to find the

several volatile deposits and lot of valuable minerals such as silver ,mercury, helium

on the portions of moon where there is no sunlight for several lakhs of years.


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Chapter 4

Comparison of Mini RF Technology with other Radar

SystemsTable 1. Radar System Comparisons with Mini RF Technology

Table 2. Communications System Comparison with Mini RF Technology


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Chapter 5

Mini-RF Instrument Description

The Mini-RF observations are made possible within the mass and power constraints

imposed by LRO via application of a number of technologies. Two key technologies

are a wideband Microwave Power Module (MPM) based transmitter and a lightweight

broadband antenna and polarization design.

The Mini-RF Instrument is comprised of the following elements:

(1) Antenna,

(2) Transmitter,

(3) Digital receiver/quadrature detector waveform synthesizer,

(4) Analog RF receiver,

(5) Control Processor,

(6) Interconnection module

(7) Supporting harness, RF cabling, and structures.


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Figure.2 The LRO Mini-RF system functional block diagram


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5.1Hybrid-polarity architecture

Figure 3. Hybrid-polarity architecture


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The mini RF architecture is unique in planetary radar; it transmits right circular

polarization radiation and receives the horizontal (H) and vertical (V) polarization

components coherently, which are then reconstructed as Stokes’ parameters during the

data processing step. Both the communications and the radar astronomical objectives

impose a requirement for circular polarization on the transmitted field. Conventional

radar that would measure CPR then would have to be dual-circularly polarized on

receiver. The hybrid-polarity approach provides weight savings by eliminating

circulator elements in the receiver paths, which reduces mass, increases RF efficiency,

and minimizes cross-talk and other self-noise aspects of the received data. The H and

V signals are passed directly to the ground-based processor. It is well known that the

Stokes parameters comprise a full characterization of the backscattered field. The

values of the four Stokes parameters do not depend on the choice of receiver

polarization, so this architecture minimizes hardware while maintaining full science

value. The result provides significant advantages over the conventional “CPR-

measuring” dual-circular-polarized approach, yet the radar is simpler. The use of

possible Stokes parameter-based products (e.g. CPR, degree of- depolarization,

degree-of-linear-polarization, and phase “double bounce”) have a number of

significant advantages over traditional radar systems: less hardware is needed,

resulting in fewer losses and a “cleaner,” simpler flight instrument. The signal levels

are comparable (within ∼2 dB) in both channels allowing relatively relaxed

specifications on channel-to channel cross-talk and more robust phase and amplitude

calibration. The processor has a direct view through the entire receiver chain;

including the antenna receives patterns and other radar parameters (e.g., gain and

phase). These parameters are applied in processing “Levels” (Level 0, 1) which

correspond to successive data processing stages. The design allows selective Doppler

weighting to maximize channel–channel coherence (e.g., reduce the H & V beam

mismatch). As CPR is less sensitive to channel imbalance by at least a factor of 2 with

respect to explicit RCP/LCP, Stokes parameter-based backscatter decomposition

strategies can help distinguish “false” from “true” high CPR areas. The hybrid-polarity

approach provides weight savings by eliminating circulator elements in the receiver

paths, which reduces mass, increases RF efficiency, and minimizes cross-talk and


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other self-noise aspects of the received data. The H and V signals are passed directly

to the ground-based processor. It is well known that the Stokes parameters comprise a

full characterization of the backscattered field. The values of the four Stokes

parameters do not depend on the choice of receiver polarization, so this architecture

minimizes hardware while maintaining full science value.

The result provides significant advantages over the conventional “CPR measuring”

dual-circular-polarized approach, yet the radar is simpler. The use of possible Stokes

parameter-based products (e.g. CPR, degree of-depolarization, degree-of-linear-

polarization, phase “double bounce”) have a number of significant advantages over

traditional radar systems: less hardware is needed, resulting in Fewer losses and a

“cleaner,” simpler flight instrument. The signal levels are comparable within 2 dB)

in both channels allowing relatively relaxed specifications on channel-to channel

cross-talk and more robust phase and amplitude calibration. The processor has a direct

view through the entire receiver chain; including the antenna receives patterns and

other radar parameters (e.g., gain and phase). These parameters are applied in

processing “Levels” (Level 0, 1) which correspond to successive data processing

stages. The design allows selective Doppler weighting to maximize channel–channel

coherence (e.g., reduce the H & V beam mismatch). As CPR is less sensitive to

channel imbalance by at least a factor of 2 with respect to explicit RCP/LCP, Stokes

parameter-based backscatter Decomposition strategies can help distinguish “false”

from “true” high CPR areas. Compact polarimetric encompasses those options that fall

between dual-polarized and quad-pole SARs. Compact polarimetric radars transmit on

only one polarization, and receive on two orthogonal polarizations, retaining their

relative Phase. In the radar remote sensing world assumed to include only linearly

polarized systems, coherent dual-polarimetric imaging radar was disregarded.

However, if alternative transmit polarizations (such as circular or 45_ linear) are

considered, then compact polarimetric radars deserve recognition as a potentially

important SAR option. The major motivation for compact polarimetric is to strive for

quantitative backscatter classifications of the same finesse as those from a fully

polarized system, while avoiding the principal disadvantages (mass, power, and

limited coverage) associated with a quad-pole SAR.


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5.2 Antenna

An “egg crate” antenna allows a broadband, dual-frequency design with a single

antenna panel, without any deployable mechanisms (e.g. feeds) while also meeting

stringent weight and volume constraints. The elements are sized to allow a 3:1

frequency range. Each element incorporates radiators and physical phasing combines

their power. The thermal design, materials selection, manufacturing, and test

qualification heritage of single-frequency Chandrayaan Mini-SAR antenna was

applied to the dual frequency LRO Mini-RF unit. Because of this heritage, the Mini-

RF antenna is robust and lightweight (4 kg) while satisfying all technical

requirements.

Figure.4 Mini-RF antenna design


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5.3 Transmitter

The LRO Mini-RF transmitter takes full advantage of the capabilities of the wideband

antenna. The transmitter is the first implementation of Microwave Power Module

(MPM) technology on a long-duration spaceflight, which affords a significant

breakthrough in available bandwidth and power efficiency with reduced mass as

compared to previous traveling wave tube (TWT) systems. The MPM combines a

solid state RF driver/preamplifier with a traveling wave tube amplifier, a hybrid

approach combining the advantages of both solid state and vacuum electronic

technology. Flight-testing the MPM technology is a major goal of the Mini-RF

demonstration. The MPM is enabling in giving Mini-RF its dual band capability

within the challenging mass, power, and volume constraints of the LRO spacecraft.

MPM technology has extensive heritage in airborne and other tactical systems but the

Mini-RF development program had to make significant efforts to qualify it for

spaceflight. The transmitter consists of a low-voltage CCA, high-voltage potted

assembly, solid-state driver amplifier, and a miniature helix TWT. A

compartmentalized EMI filter is also included in the transmitter, along with an RF

power monitor port with analog voltage output for power sensing and control. The

highly integrated nature of MPMs allowed for the implementation of several control

features to achieve the multi-mode, multi-band requirements for the Mini-RF

transmitter.


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Figure.5 Mini-RF transmitter block diagram


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Figure.6 Mini-RF Microwave Power Module Traveling Wave Tube (MPM/TWT)

The primary Mini-RF transmitter challenge is adapting these proven airborne designs

for space application. These include materials and part selection, out gassing,

reliability, and radiation tolerance. The technical challenges overcome in the

transmitter included developing low out gassing, high voltage insulators and space

qualification parts screening for miniature high-voltage power supplies. The

transmitter complied with the overall Mini-RF parts screening program which

screened parts to a total dose of 20 kRad, no destructive latch-up, and tolerance of

non-destructive latch up at 75 MeV. Meeting the stringent mass and power

limitations required some parts to carry wavers but the overall parts’ program was

compatible with the Class S and LRO Class B requirement with de-rating criteria in

accordance with established procedures. Mini-RF uses PEMs (Plastic Encapsulated

Microcircuits) with the screening operable over the temperature range of −55 to

+125°C. The MPM thermal design necessitated integration with the LRO heat-pipe

system, which allowed for effective dissipation of heat generated by the transmitter.


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5.4 Interconnect Module

The Interconnect Module (IM) combines and splits the RF energy and serves as the

interface between the transmitter, receiver, and antenna. Its design specifically handles

issues such as multination using selected materials and geometry.

5.5 Receiver

LRO’s receiver section is consisting of analog RF receiver and digital

receiver/quadrature detector waveform synthesizer. Receiver section is responsible for

receiving signals transmitted from the Mini RF transmitter and also responsible to

carryout required operations. Analog receiver is responsible for down conversion of

RF to IF and provides gain control. Digital receiver is responsible for digitalize the IF.

The digital receiver and quadrature digital waveform synthesizer (QDWS), based on

airborne radar heritage, were adapted to lunar orbital requirements. These systems

enabled the flexibility and reprogrammability required by the mini-RF system in

LRO’s low-altitude lunar orbit.

5.6 Control Processor

Control Processor is responsible for coordinating the entire functions Mini RF

system. Functions of Control Processor are digitizing antenna temperature, accept

commands from bus electronics, control and configure payload electronics and

provide router interface from digital receiver to bus electronics for radar data.


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Chapter 6

Calibration

Polari metric measurements imply more stringent calibration of the radar than required

by a single channel system; since quantitative Polari metric measurements depend on

the relative phase and magnitude between signals in the two receive channels. Hybrid–

polar metric architecture has the unique and appealing property that it is self calibrating.

Calibration of the mini-RF instruments proved challenging for several reasons. Prior to

launch no opportunities for end-to-end measurements of the complete radar system

were available; only standalone characterizations of the radar electronics and antenna

were possible. Once in flight, conventional calibration techniques used by Earth orbiters

.The mini-RF calibration campaign included direct and separate characterizations of the

transmit and receive portions of the radars via Earth-based resources, hence obviating

the assumption of perfect circularity of the transmitted signal from the calibration

analysis. The two mini-RF radars are the pioneers of this calibration strategy. The on-

orbit calibration experiments measured the mini-RF receive and transmit characteristics

on separate days, using different Earth-based antennas, as the corresponding transmitter

or receiver platforms. The Arecibo Radio Telescope (ART) in Puerto Rico acted as a

transmitter to the mini-RF receiver. The Green Bank (Radio) Telescope (GBT) in West

Virginia received mini-RF transmissions. For both sessions; the spacecraft was

maneuvered to generate cross sections of the elevation and azimuth antenna patterns.

Effects due to the Earth’s ionosphere proved to be negligible. In a separate operation,

the spacecraft was rolled to point the radar antenna towards the Moon at nadir. In this

orientation, the expected radar backscattering properties in the H and V polarizations

are known to be (on average) the reflection of the transmitted signal, comprising a

practical means of collecting an end-to-end data set of known characteristics.


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Chapter 7

Data analysis and Interpretation

Following in-flight calibration, a set of coefficients will be derived and applied to the

radar data as part of the standard processing stream prior to computing the Stokes

parameters that in turn are used to calculate daughter products (e.g. CPR, degree of

linear and circular polarization). A joint Chandrayaan/LRO Mini-RF Payload

Operations Center (POC) is located at APL to support the Mini-RF experiments. The

POC will provide the following functions: forward data acquisition sequences to

GSFC, receive raw telemetry from GSFC, process raw telemetry, produce mosaics,

and catalog data for the PDS and other repositories. The POC team is comprised of the

POC lead engineers, Science Team representatives and the POC engineers. The

Calibration and Collect commands have embedded argument lists that configure the

radar with respect to waveform, pulse repetition frequency (PRF), pulse width, burst

time, burst duty factor, number of bursts, and position of receiving gate, bandwidth,

start frequency, and other supporting parameters. Once the acquired data and the

required ancillary data have been received by the POC, the data will be processed

according to the data type. This processing will use the ephemeris data supplied to the

POC to create products to be checked for completeness and quality. To calculate the

circular polarization ratio of the received signal (CPR = SC/OC), we must be able to

calculate the total power returned in the same polarization as was transmitted

(SC = ∣EH∣2) and the total power returned in the opposite polarization (OC = ∣EV∣2).

These values can be expressed in terms of the Stokes vector, which represents the time

averaged Polarization properties of the backscattered field .It is a straightforward

matter to determine the Stokes vector from the total power received in the H and V

channels and the real and imaginary parts of their complex conjugate, HV* Circular

polarization ratios can then be calculated from the Stokes vectors.


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For example, CPR = SC/OC = (S1 − S4)/ (S1 + S4), where S1 represents the total

received power, S1=[|E(H)|^2+ |E(V)|^2],

S2= =[|E(H)|^2-|E(V)|^2],S3=2Re[E(H)E(V)*] and

S4=-2Im [E (H) E (V)*] =.It is possible to derive lot daughter products from stock

parameters such as , , m, .where m is degree of polarization

m=sqrt(S2^2+S3^2+S4^2)/S1;

is circular polarization ratio = (S1-S4)/(S1+S4); is linear polarisation ratio

=(S1-S2)/(S1+S2); is relative phase =arctan(S1/S2).

Figure 7 Mini-RF calibration strategies


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Chapter 8

Stokes Parameters as clear evidence of lunar ice

Stokes parameters as described earlier, are useful tools to study the scattering

properties of various features on the lunar surface. The magnitude and sense of

polarization of the reflected signal associated with various lunar morphological

features as well as water-ice inside the craters were examined using Mini-SAR data.

Traditionally, the key parameter used to determine whether ice is present is the CPR.

CPR was used in the present study to find evidence of subsurface scattering due to

dielectric in homogeneities like water-ice. Apart from high CPR, parameters like

degree of polarization (m) and relative EH–EV phase (δ) are also important

parameters to study the scattering mechanisms associated with lunar ice. The m–δ

together indicate the type of scattering mechanism associated with the target, because

at higher m value (m > 0.5), δ values close to –90° and +90° indicate surface and

double bounce scatterings respectively, and all other values of δ indicate diffused

scattering mechanism. The problem with using CPR alone is that higher values can be

obtained from very rough surfaces, such as a rough, blocky lava flow, which has

angles that form many small corner reflectors. In this case, the radar signal could hit a

rock face (changing LCP into right circular polarization (RCP)), and then bounce over

to another rock face (changing RCP back into LCP) and hence to the receiver. This

double bounce effect also creates high CPR in that ‘same sense’ reflections could

mimic the enhanced CPR one gets from ice targets. Hence, the CPR values estimated

from Mini-SAR have been analyzed along with m and δ values for indicating the

presence of water-ice

Table 3.

Daughter Products Derivation Significance

Degree of polarisation (m)

m=sqrt(S2^2+S3^2+S4^2)/S1 Indicator of polarized and diffused scattering; related to entropy

Linear polarisation ratio ( )

=(S1-S2)/(S1+S2) Indicator of volume v/s sub surface scattering

Circular polarisation ratio (

)=(S1-S4)/(S1+S4) Indicator of scattering lunar ice deposits

Relative phase ( ) = arctan(S1/S2)Indicator of double bounce scattering


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Chapter 9

Applications

The Lunar Reconnaissance Orbiter (LRO) Mini-RF technology is the product of over

a decade of development. Its objectives are: (1) Flight verification of an advanced

lightweight RF technology for future NASA and DoD communications applications;

(2) Demonstration of a hybrid-polarity Synthetic Aperture Radar (SAR) architecture;

(3) Obtaining measurements of the lunar surface as a function of radar band (S and X)

and resolution (150 m, 30 m) which could identify water ice deposits in the

permanently shadowed polar regions; (4) Production of topographic data using

interferometry (S-band) and SAR stereo techniques; and (5) Mapping of areas of

interest identified by the Chandrayaan-1 Forerunner Mini-SAR experiment and other

lunar instruments. Because Mini-RF provides its own illumination and can penetrate

the near subsurface at meter scales, it will acquire data not obtained by any other LRO

payload. Over the previous decade, the Department of Defense (DoD) and commercial

industry made significant strides in developing advanced lightweight RF technology

for wireless communication, Unmanned Airborne Vehicles (UAVs), and tactical

missiles. The first, “Forerunner” Miniature SAR (Mini-SAR), was developed and

integrated into the Indian Space Research Organization which is Chandrayaan. The

ForerunnerMini-SAR had to operate in the lunar thermal and radiation environment,

yet was simpler in design and operation, providing significant experience and

reduction of risk for the more advanced LRO Mini-RF system. The LRO Mini-RF

affords NASA and the DoD an opportunity to flight-qualify lightweight technology

for a range of applications, including deep space communications. The flexibility,

reconfigurability, and capability of Mini-RF will be demonstrated by a

communications and radar mode utilizing the same hardware. The constraints of a

lunar mission (range, limited duty cycle over the poles) and the low mass of advanced

lightweight RF technology allows a technology demonstration which met the payload

constraints of both the Chandrayaan and LRO spacecraft, and provided an opportunity

to collect unique and valuable lunar science data.


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Chapter 10

Conclusion

The mini-RF radars on the LRO have proven to be very successful, meeting or

exceeding their design requirements and expectations. Their hybrid – polarity

architecture is the first demonstration of this design paradigm from orbit. They afford

the first polarimetric radar observations of the entire Moon, including especially the

lunar poles and far side. The results are providing new information and opening new

insights into the lunar surface. From a technical point of view, the mini-RF radars

have pioneered several innovations. They have been exercised in unique calibration

modes that do not depend on the usual in situ references of an extended distributed

backscattering feature (such as the Amazon rain forest) or a Calibrated point reference

(such as a corner reflector or active radar calibrator). For lunar or planetary

polarimetric radars, calibration methodologies are required that do not require known

references in the scene. By taking advantage of the polarization basis independence of

the Stokes parameters of the received data, the mini-RF systems are more capable

instruments than all previous radars that have ventured outside Earth orbit, yet their

implementation is relatively simple, an attribute that is especially appealing for

planetary deployments. Although for both radars the observed transmitted field is

elliptically polarized rather than purely circular, simple polarimetric analysis such as

estimation of CPR seems relatively robust to this imperfection. Other Stokes-based

measurements may be more sensitive to imperfect circularity of the illuminating field.


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Chapter 11

References

1. www.spudislunarresources.com

2. www. lunar.gsfc.nasa.gov

3. www. ieeexplore.ieee.org

4. Ritchriya

5. NASA Fact


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Cmplt Seminar Report - Copy