Mod

ern

radi

o te

chni

ques

for

prob

ing

the

iono

sphe

re

Cesi

dio

Bian

chi I

NGV

- R

oma

Ital

y

Rece

iver

, rad

ar, a

dvan

ced

iono

sphe

ric

soun

der,

and

rel

ated

tech

niqu

es

Iono

sphe

ric

prop

erti

es r

elat

ed t

o ra

dio

wave

sTh

e m

ost

usef

ul

way

to p

erfo

rm s

yste

mat

ic m

easu

rem

ents

inth

e io

nosp

here

is

to

use

radi

o wa

ves.

Thi

s ca

n be

don

eex

ploi

ting

the

pro

pert

ies

of t

he i

onos

pher

e wh

en it

int

erac

tsin

var

ious

way

s w

ith

the

elec

trom

agne

tic

wave

s.

The

radi

o te

chni

ques

for

pro

bing

the

iono

sphe

re a

re s

prea

d in

near

ly a

ll ra

nges

of

radi

o fr

eque

ncy.

We

expl

ore

the

str

uctu

re

of

the

iono

sphe

re

by

boun

cing

radi

o wa

ves

of d

iffe

rent

fre

quen

cies

on

it, a

nd u

sing

spe

cial

rece

iver

s to

det

ect

how

the

ref

lect

ed w

aves

hav

e c

hang

edfr

om t

he t

rans

mit

ted

wa

ves.

We

als

o ex

amin

e t

he

chan

ges

of

the

rad

io w

aves

fr

omsa

telli

tes

tran

smit

ted

thro

ugh

the

iono

sphe

re e

tc..

Tech

niqu

es

- ve

rtic

al s

ound

ings

+ D

oppl

er s

hift

mea

sure

men

t

- in

cohe

rent

sca

tter

rad

ar

- TE

C m

easu

rem

ent

•Th

e ra

dio

is a

dev

ice

that

eit

her

gene

rate

s, o

rre

spon

ds t

o r

adio

wav

es.

•Th

e ra

dar

(rad

io d

etec

tor

and

rang

ing)

is

a de

vice

able

to

tran

smit

a p

ulse

d ra

dio

wave

and

rec

eive

its

echo

eva

luat

ing

also

the

ran

ge a

nd t

he m

odif

icat

ion

of t

he t

rans

mit

ted

rad

io w

ave.

Radi

o &

Rada

r p

rinc

iple

s

Basi

c re

quir

emen

ts f

or r

ecei

vers

:

- R

ecei

ving

, am

plif

ying

and

dem

odul

atin

g

AM

, FM

, ph

ase

code

d wa

ves,

etc

.

–ab

ility

to

tune

to

a sp

ecif

ic s

igna

l

–am

plif

y th

e si

gnal

tha

t is

pic

ked

up

Radi

o Re

ceiv

er

Supe

rher

odyn

e re

ceiv

er

sect

ions

func

tion

s &

requ

irem

ents

-m

odul

atio

n (am

plit

ude,

fre

quen

cy, p

hase

etc

..) (i

nfor

mat

ion)

-fi

lter

(s

elec

tivi

ty)

-am

plif

ier

(dyn

amic

, sen

siti

vity

and

line

arit

y)

-de

tect

ion

(dyn

amic

and

line

arit

y)

- co

ntro

l (dy

nam

ic a

nd li

near

ity,

AGC

, sel

ecti

vity

)

ante

nna

A r

adio

ant

enna

may

be

defi

ned

as a

str

uctu

reas

soci

ated

wit

h th

e re

gion

of

tran

siti

on b

etwe

ena

guid

ed w

ave

and

free

spa

ce o

r vi

ce v

ersa

(Kra

us)

RF f

ront

-end

Inte

rmed

iate

fre

quen

cy

Mix

er-

By

a lo

cal o

scill

ator

LO

, the

RF

is c

onve

rted

to

IF (R

F to

IF

tran

slat

ion)

. Sha

pe o

f th

e en

velo

pe r

emai

n th

e sa

me.

BW

is u

ncha

nged

–IF

is c

hose

n al

ways

lowe

r th

an R

F:m

ore

stab

le (d

o no

t os

cilla

te).

Usu

ally

one

RF a

mpl

ifie

r, I

F st

ages

>2

Det

ecti

on p

roce

ss

Det

ecti

on

Two

type

s•

Cohe

rent

(syn

chro

nous

): fr

eque

ncie

sus

ed f

or d

emod

ulat

ion

are

exac

t co

pyof

Tx

carr

ier

•N

on-c

oher

ent

(asy

nchr

onou

s):

enve

lope

det

ecti

on

Inte

rnal

noi

se

The

whit

e n

oise

is d

ue t

o th

e ra

ndom

mot

ion

of t

heel

ectr

ons.

The

vol

tage

acr

oss

the

two

resi

stor

ter

min

alat

the

abs

olut

e te

mpe

ratu

re T

is:

Vrm

s=2(

KTRB

)0.5

whe

re K

is t

he B

oltz

man

n co

nsta

nt (J

/Hz)

and

B is

the

ban

d of

fre

quen

cy c

onsi

dere

d.U

nder

wel

l mat

ched

con

diti

on t

he p

ower

is P

=KTB

(W)

By d

efin

itio

n th

e no

ise

fact

or F

is:

Sign

al-t

o-no

ise

rati

o(in

put)

/ S

igna

l-to-

nois

e ra

tio

(out

put)

Inte

rnal

noi

se 2

In t

he r

ecei

ver

it is

use

ful t

o de

fine

the

noi

se f

acto

rF

in q

uant

itat

ive

way

as:

wher

e P i

and

PA a

re t

he in

put

nois

e a

nd a

ddit

iona

lno

ise

mea

sure

d at

am

plif

ier

the

outp

utTh

e no

ise

figu

re is

f noi

se =

10

log 1

0 F

)o

/(/

APB

GKT

GPi

KToB

PiF

+=

envi

ronm

ent

nois

e &

inte

rfer

ence

s

•W

hat

is im

port

ant

at t

he a

nten

na le

vel i

s th

e si

gnal

-to

-noi

se r

atio

(S/N

)•

The

nois

e le

vel d

oes

not

allo

w to

incr

ease

the

sens

itiv

ity

as w

e de

sire

.

•Te

rres

tria

l env

iron

men

t is

con

tinu

ousl

y ex

pose

d to

elec

trom

agne

tic

radi

atio

ns, w

hich

set

up

a“b

ackg

roun

d ” o

f el

ectr

omag

neti

c no

ise.

The

elec

trom

agne

tic

back

grou

nd r

efer

s to

the

envi

ronm

ent

in w

hich

the

re a

re b

oth

natu

ral a

ndm

anm

ade

elec

trom

agne

tic

nois

e.

•Br

oadc

asti

ng s

tati

ons

can

caus

e st

rong

inte

rfer

ence

s wh

ich

affe

ct t

he r

ecep

tion

of

the

sign

al

Rada

r

TX

R XRe

ceiver

CCo

ntro

ller

Display

unit

T/R

switch

or

circ

ulat

or

Mon

o st

atic

rad

ar

Bi-s

tati

c ra

dar

Freq

uenc

y sy

nthe

size

r

DD

S

Rad

ar e

quat

ion

The

rada

r eq

uati

on r

epre

sent

s th

e ph

ysic

al d

epen

denc

es o

fbe

twee

n th

e tr

ansm

itte

d p

ower

and

rec

eive

d po

wer.

432 )

4()

(rP

GP

rad

dr

πσ

λ=

Rad

ar e

q

Var

iabl

eD

efin

ition

Uni

ts

P rPo

wer

rece

ived

by

the

rada

ran

tenn

aw

atts

(W)

λW

avel

engt

h of

sign

al re

ceiv

ed b

y ra

dar a

nten

nam

eter

s (m

)

Gd

Dire

ctiv

e ga

in o

f ant

enna

(mea

sure

of t

heco

ncen

tratio

n of

the

radi

ated

pow

er in

a p

artic

ular

dire

ctio

n)

unitl

ess

σRa

dar

cros

s se

ctio

n (c

hara

cter

izes

the

targ

et’s

abi

lity

to s

catt

er o

r re

flec

t en

ergy

)sq

uare

met

ers

(m2 )

P rad

Powe

r di

ssip

ated

thr

ough

the

cha

ract

eris

tic

impe

danc

e, R

rad,

of

the

TX r

adar

ant

enna

wat

ts (W

)

rD

ista

nce

mea

sure

d fr

om t

he r

adar

to

the

targ

etm

eter

s (m

)

43

2 )4(

)(

rPG

Prad

dr

πσ

λ=

Rada

r cr

oss

sect

ion

•Ra

dar

cros

s se

ctio

n is

def

ined

as:

2

24

=is

EEr

πσ

wher

e E s

and

Ei

are

defi

ned

as t

he s

catt

ered

and

inc

iden

tel

ectr

ic f

ield

s, r

espe

ctiv

ely.

Es

is m

easu

red

at t

he r

ecei

ving

ante

nna,

whe

reas

Ei i

s m

easu

red

at t

he t

arge

t le

vel

. Si

nce

the

scat

tere

d el

ectr

ic

fiel

d is

in

vers

ely

prop

orti

onal

to

dist

ance

, r, t

he r

adar

cro

ss s

ecti

on r

educ

es t

o th

e fo

llowi

ng:

2

2

24

4

=

≡is

is

EEErE

rπ

πσ

iono

sond

es 1

Enve

lope

det

ecto

r io

noso

nde

or H

F Ra

dar

iono

sond

e bl

ock-

diag

ram

Del

ay

- Th

e fr

eque

ncy

mea

sure

men

t is

ass

ured

by

the

rece

iver

sel

ecti

vity

alw

ays

tune

d wi

th t

hetr

ansm

itte

d fr

eque

ncy

In p

ract

ical

is t

he s

ame

freq

uenc

y sy

nthe

size

rth

at s

teer

s bo

th t

rans

mit

ter

and

rece

iver

2

•Ve

rtic

al s

ound

ing

are

perf

orm

ed b

y a

high

freq

uenc

y ra

dar

know

n as

io

noso

nde.

Th

eio

noso

nde

send

s sh

ort

puls

es o

f ra

dio

ener

gyve

rtic

ally

into

the

iono

sphe

re. T

hese

pul

ses

are

refl

ecte

d ba

ck t

owar

ds t

he g

roun

d an

d th

eio

noso

nde

reco

rds

the

tim

e de

lay

betw

een

tran

smis

sion

an

d re

cept

ion

of

puls

es.

Byva

ryin

g th

e ca

rrie

r fr

eque

ncy

of p

ulse

s fr

om 1

to

20

MH

z,

the

tim

e de

lay

at

diff

eren

tfr

eque

ncie

s is

rec

orde

d.

Vert

ical

sou

ndin

g

Mag

neto

plas

ma

sepa

rate

the

wav

e in

to t

woco

mpo

nent

s

fp, ν

and

fB

- th

e pl

asm

a fr

eque

ncy

fp is

:

02

21

επmNe

f p=

-The

fre

quen

cy o

f co

llisi

on b

etwe

en e

lect

rons

and

neu

tral

mol

ecul

es ( ν

)

is:

ν=1

/ τ b

eing

τ is

the

ave

rage

tim

e be

twee

n c

ollis

ions

   -fre

quen

cy o

f cy

clot

ron

( fB) 

f B =

e B

/ m

2π

  esta

blis

hes

the

cond

itio

n of

pro

paga

tion

of

the

wave

thro

ugh

the

mag

neti

sed

iono

sphe

ric

plas

ma.

Iono

sphe

ric

plas

ma

iono

gram

Iono

gram

’s ch

arac

teri

stic

s

Bott

om p

rofi

le (p

ost-

proc

ess)

Puls

e co

mpr

esse

d io

noso

ndes

C

hirp

: typ

ical

pha

se c

odin

g or

mod

ulat

ion

appl

ied

to t

hera

nge

puls

e of

a r

adar

des

igne

d to

ach

ieve

a la

rge

ti

me-

band

widt

h pr

oduc

t. T

he r

esul

ting

pha

se is

qua

drat

ic in

tim

e, w

hich

has

a li

near

der

ivat

ive.

Suc

h co

ding

is o

ften

calle

d lin

ear

freq

uenc

y m

odul

atio

n, o

r lin

ear

FM.

•Th

e m

ost

sign

ific

ant

adva

ntag

es o

f th

e ch

irp

tech

niqu

esov

er o

ther

pul

se H

F sy

stem

are

:•

the

redu

ced

vuln

erab

ility

to

narr

ow-b

and

inte

rfer

ence

•th

e us

e of

low

powe

r du

e to

the

abi

lity

to t

rans

mit

wit

h a

near

ly u

nit

duty

cyc

le.

CHIR

P

Chir

p m

odul

atio

n (C

W-F

M)

Chir

p io

noso

nde

Chir

p te

chni

ques

1

Chir

p te

chni

ques

2

• F

requ

ency

ana

lysi

s of

the

de-

chir

ped

sign

al is

know

n to

be

iden

tica

l to

a m

atch

ed f

ilter

in p

ulse

com

pres

sion

rad

ar. T

he p

ulse

com

pres

sion

rat

io G

is g

iven

by: 

G =

BT

w

here

B is

the

fre

quen

cy s

weep

ran

ge a

nd T

isth

e ti

me

dura

tion

for

one

spe

ctru

m a

naly

sis]

.Ra

nge

reso

luti

on ∆

r is

giv

en b

y: 

∆r

= c

/ 2B

w

here

c is

the

vel

ocit

y of

ligh

t.

Obl

ique

sou

ndin

g

Obl

ique

iono

gram

Phas

e-co

ded

iono

sond

e

Code

gen

erat

ion

base

band

Tim

e-do

mai

n co

rrel

atio

n

Puls

e co

mpr

essi

on

The

phas

e pa

th P

is g

iven

by

Proc

essi

ng g

ain

•M

ore

or le

ss 3

0 dB

•A

bout

15

dB d

ue t

o co

rrel

atio

npr

oces

s

•A

bout

15

dB d

ue t

o ph

ase

cohe

rent

inte

grat

ion

The

reco

nstr

uction

of

the

code

, ba

seba

nd,

star

ting

fro

m t

he e

cho

sign

al is

the

follo

wing

:•the

ana

log

sign

al a

t th

e ou

tput

of

the

IF (

typica

lly 1

00 k

Hz)

is

sampled

bot

h in p

hase

and

quad

ratu

re a

t th

e sa

me

freq

uenc

y•the

qu

adra

ture

sam

pling

allows

to

obta

in t

heam

plitud

e an

d, m

ore

impo

rtan

t, t

he ph

ase

of t

hesign

al t

o re

cons

truc

t th

e ba

seba

nd•a

fter

the

A/D

con

vers

ion

the

signa

l is f

edth

roug

h th

e digita

l mat

ched

file

r im

plem

ente

d on

the

DSP

boa

rd•the

pro

cess

is

repe

ated

for

the

eve

n an

d od

dco

de if

complem

enta

ry c

ode

is u

sed.

Code

rec

onst

ruct

ion

Com

plem

enta

ry c

ode

In t

he c

ompl

emen

tary

pha

se c

ode

the

sid

e lo

bes

of t

heco

rrel

atio

n pr

oces

s an

d in

a c

erta

in m

easu

re t

he n

oise

supe

rim

pose

d to

the

sig

nal

16.0

0272

7

3.01

0122

u1l

u2l

240

180

l18

019

020

021

022

023

024

010

0

1020

l

32.0

0177

6

0.04

5786

u1l

u2l

180

190

200

210

220

230

240

2002040

Pu

lse

compr

ession

tec

hnique

The

ener

gy (E

) of

the

echo

sig

nal f

rom

the

iono

sphe

re, u

nder

cert

ain

prop

agat

ive

cond

itio

n, i

s pr

opor

tion

al t

o th

etr

ansm

itte

d po

wer

(P) a

nd t

he p

ulse

leng

th (T

)E=

P ⋅T

In t

he o

ld io

noso

nde

the

powe

r P

was

of t

he o

rder

of

1000

0W

whi

le t

he p

ulse

leng

th, t

o ha

ve t

he d

esir

ed h

igh

reso

luti

on, w

as 3

0 µs

, so

the

ener

gy w

as o

f th

e or

der

of 0

.3J. Th

e ph

ase

code

d H

F ra

dar

uses

a p

ulse

leng

th o

f ab

out

500

µs a

nd a

pow

er o

f 20

0 W

and

the

ene

rgy

of t

he p

ulse

is 0

.1 J

(sam

e or

der

of m

agni

tude

). T

he r

esol

utio

n is

mai

ntai

ned

beca

use

an a

dequ

ate

num

ber

of s

ub-p

ulse

τ c

onst

itut

e th

epu

lse

leng

th T

.

1

•Th

e pa

rtic

ular

seq

uenc

e of

the

sub

-pul

ses

that

is w

hat

we s

ay a

cod

e.

The

puls

eco

mpr

essi

on c

onsi

sts

to in

put

the

puls

e T

(sub

puls

e se

quen

ce) i

n a

mat

ched

filt

er,

whic

h is

sen

siti

ve o

nly

to t

he c

hose

n co

de,

whos

e ou

tput

con

cent

rate

its

ener

gy in

ati

me τ.

•So

the

mat

ched

filt

er m

agni

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