Derived Backscatter Values from JERS-1 Digital Number Distributions Over Ross Island, Antarctica

(McMurdo Station)

(j'o (j'o

0

(j' (j' 0 (j' 0

McMurdo Station - 0 (j'

T W f Ott!O ST .-. TE UNIII'E R S !l V

· ...

Compiled in 1996 by the

BYRD POLAR RESEARCH CENTER

This report may be cited as:

Noltimier, Katy F. , Hong-Gyoo Sohn, and Kenneth C. Jezek. 1996. DerivedBackscaner Values From JERS-1 Digital Number Distributions Over Ross Island, Antarctica (McMurdo Station). BPRC Technical Note No. 96-01 , Byrd Polar Research Center, The Ohio State University, Columbus, Ohio, 12 pages.

The Byrd Polar Research Center Report Series is edited by Lynn Tipton-Everett.

Copies of tills and other publications of the Byrd Polar Research Center are avai lable from:

Publication Distribution Program Byrd Polar Research Center The Ohio State University

1090 Carmack Road Columbus, Ohio 43210-1002

Telephone: 614-292-6715

DERIVED BACKSCA TIER VALUES FROM JERS-1 DIGITAL NUMBER DISTRIBUTIONS OVER ROSS ISLAND,

ANTARCTICA (MCMURDO STATION)

Katy F. Noltimier, Hong-Gyoo Sohn, and Kenneth C. Jezek

Byrd Polar Research Center The Ohio State University

Columbus, Ohio

Byrd Polar Research Center, The Ohio State University Columbus, Ohio 43210

BPRC Technical Note 96-01

TABLE OF CONTENTS

Table of Contents ............. .... ............. ....... ... ................ .................... .... ....... iii

Abstract. ........................ ........................... .................. ................................ v

1.0 Introduction........................................ .............................................. .... 1

2.0 Derived Backscatter Values from JERS-1 Digital Number Distributions................. ........ ........ .. .. ..... ... .. ....... ................. .... ..... .... ...... . 1

2.1 Procedure.. .... ..................................................... .. .......................... ...... 1

2.2 Discussion.. ......................... ............ ........ ......... .. ... .............. ................. 2

References ... .......... ....... .... ..... ... ........................ ..... ....... .. ......... ................. .. 3

Apendix ................ .... .... ... ... ........ ......................... ....................... .... ...... ...... 4

iii

ABS1RACT

This report examines the derived backscatter values for different physical

properties from one JERS-1 image over Hut Point Peninsula on Ross Island in the

McMurdo Station area. The results discussed in this report will be used to determine a

suitable location for transponder testing for the Radarsat Antarctic Mapping Project.

Histograms of digital number (DN) values (0-255) were created to determine the

DN distribution and approximate backscatter value for five locations on a single JERS-1

image. Two locations were chosen over first year sea ice, and one location each over

glacial ice, exposed rock, and the McMurdo Station. From published backscatter values

for first year ice of -15dB and a DN of 40, estimated from histograms, an approximation

of the calibration constant K was calculated and subsequent backscatter coefficients were

computed for the remaining locations. Digital numbers peaked at 255 for both glacial ice

and McMurdo Station indicating that an area outside of McMurdo Station would be

preferable for transponder testing.

v

DERIVED BACKSCA TIER VALUES FROM JERS-1 DIGITAL NUMBER DISTRIBUTIONS OVER ROSS ISLAND,

ANTARCTICA (MCMURDO STATION)

1.0 IN1RODUCTION:

This report examines the derived backscatter values for different physical

properties from one JERS-1 image over Hut Point Peninsula on Ross Island in the

McMurdo Station area. The JERS-1 SAR operates at L-band, HH polarization, and with

a viewing geometry (incidence angle) of 40°. The results discussed in this report will be

used to determine a suitable location for transponder testing for the Radarsat Antarctic

Mapping Project.

2.0 DERNED BACKSCA TIER VALVES FROM JERS-1 DIGITAL NUMBER DISTRIBUTIONS:

Histograms of digital number (0-255) values (figures 1-5) were created to

determine the digital number distribution and subsequent backscatter value for five

locations on a single JERS-1 image over Hut Point Peninsula, Antarctica (figures 6 and 7).

Two locations were chosen over first year sea ice (figures 1 and 2), and one location each

over glacial ice, bare rock, and the McMurdo Station (figures 3-5).

2.1 Procedure:

The JERS-1 image (figure 6) is a AprilS, 1995, 8-bit, 1-byte uncompressed image

obtained from ASF processed 8 m.m tape. A section of the image (figure 7) indicates

where the locations of each of the histograms (figures 1-5) were sampled from.

A backscatter value (a j for first year sea ice of -15dB (figure 8) (\)nstott, 1992)

and a digital number, DN, of 40 estimated from patch! and patch2 (figures 3 and 4) were

used to estimate the calibration constant K value as follows:

1

where,

<l >ds = 10 log (DN1). where I is the pixel illlensity and DN is the digital number

of a given pLre/ (0 -255).

Kds= 47 ± 2 .

Figure 8 shows the resulting cr 0 approximations versus digital number disoiburion for

K IID = 47 ± 2.

2.2 Discussion:

Histograms of digital number (0-255) values were created to determine the digital

number distribution and subsequent backscatter value for five locations on a single JERS-1

image over Hut Point Peninsula, Antarctica. The average digital number for first year ice

ranged from 35 to 40. The corresponding estimated cr o for first year sea ice ranged from

-15dB to -16d.B. The average digital number for bare rock was 90 with a corresponding

estimated cr o of -8dB. The digital number for both McMurdo Station and glacial ice

peaked at 255 giving an estimated cr 0 of +ldB.

The results discussed above are summarized in the following table:

Tabl~ 1

Site Average DN A v~rage cr 0 d.D_

Figure 1 (First year sea ice) 40 -15

Figure 2 (First year sea ice) 35 -16

Figure 3 (McMurdo Station) 255 + 1

Figure 4 (Glacial Ice) 255 +1

Figyre: 5 (Bar~ Rock) 9Q - 8

ForK=47

According to these results an area outside of McMurdo Station would be preferable for transponder testing.

2

REFERENCE:

Onstott, R. G., 1992. SAR and Scatterometer Signatures of Sea Ice. In F. D. Carsey (ed.). Microwave Remote Sensing of Sea Ice. A.G.U. Geophysical Monograph Series 68. 73-104.

3

APPENDIX

4 . r

patch 1-seo_ice ( -15 dB) 150 I I I I I

100 ~ -

-

0 ~=~~~~~~~~-=~~~~~~~~~~L-~~~~~~~~~~~~~~~~~ 0 50 100 150 200 250 300

Digital Number

Figure 1. Digital number (0-255) distribution of first year sea ice.

5

potch2-seo_ice ( - 15 dB) 150

100

0 50 100 150 200 250 300

Digital Number

Figure 2. Digital Number distribution of first year sea ice.

6

patch3 - McMurdo 200

150

100

0" Q) ,_. ~ 50

0 50 100 150 200 250 300

Digital Number

Figure 3. Digital number (0-255) distribution over McMurdo Station. ·

7

300

250

200

;>, (.) 150 c: Q) :J c:r Q) )..j

"""' 100

50

0

Figure4.

patch4-ice (0 dB)

50 100 150 200 250 300

Digital Number

Digital Number distribution over glacial ice.

8

10

;:... u c: Q) :J 0'

8

6

~ 4 !:Lo

2

0

f.-

1-

~

f.-

0

Figure 5 .

patch5-land I I I I I

----

.

-

-

II~ -

I I I I

50 100 150 200 250 300 Digital Number

Digital number (0-255) distribution over bare rock.

9

Figure 6. Full JERS-1 image Hut Point Peninsula area on Ross Island. Boxed area corresponds to figure 7. 10

Figure 7 . Locations of cligital number histograms (figure 1-5) where patch 1 corresponds to figure 1 and so on.

1 1

-.c 0> ::J ctS

Digital Number vs. Sigma Naught 10r-------.--------.--------.-------~------~--------.

0

-10

z -20 ctS E 0>

Ci5

-30

-40 Conversion equation: a 0cm = 10 log (DN2

)- K

-50~----~~----~------~------~-------L------~ 0 50 150

Digital Number 100 200 250 300

For a 0 = -15dB and DN = 40 (estimated from patch! and patch2), K = 47+ 2

1.3 GHz, W Polnriznlion .otr--------- -

0 {;;11111~1 • MutllynJr tc11 • Thock F1rst • Yoar leo • Pressure R1dgol

" Freahwater Lake • a=------. . ~

.. ~ -28 fl. ... _ -~~~---~----~~--~~L-~~

IS JO 60

Anglo of tnc1donco. degrees

Figure 8. The top graph represents the range of estimated backscatter (sigma naught) versus digital number for calibration constant K=47±2. The bottom graph is the source for sigma naught value used for first year ice (-15d.B) L-Band, 40° incidence angle used to estimate the calibration constant (Onstott, 1992).

12

t I I

l

r I