Derived Backscatter Values from JERS-1 Digital Number Distributions Over Ross Island, Antarctica (McMurdo Station)

Transcription

1 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

2 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 DerivedBackscaner Values From JERS-1 Digital Number Distributions Over Ross Island, Antarctica (McMurdo Station). BPRC Technical Note No , 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 available from: Publication Distribution Program Byrd Polar Research Center The Ohio State University 1090 Carmack Road Columbus, Ohio Telephone:

3 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 BPRC Technical Note 96-01

4 TABLE OF CONTENTS Table of Contents... iii Abstract.... v 1.0 Introduction Derived Backscatter Values from JERS-1 Digital Number Distributions Procedure Discussion References Apendix... 4 iii

5 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

6 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

7 where, <l >ds = 10 log (DN 1 ). 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 ± 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. Tabl~ 1 The results discussed above are summarized in the following table: Site Average DN A v~rage cr 0 d.d_ Figure 1 (First year sea ice) Figure 2 (First year sea ice) Figure 3 (McMurdo Station) Figure 4 (Glacial Ice) 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

8 REFERENCE: Onstott, R. G., SAR and Scatterometer Signatures of Sea Ice. In F. D. Carsey (ed.). Microwave Remote Sensing of Sea Ice. A.G.U. Geophysical Monograph Series

9 APPENDIX 4. r

10 patch 1-seo_ice ( -15 db) 150 I I I I I 100 ~ ~=~~~~~~~~-=~~~~~~~~~~L-~~~~~~~~~~~~~~~~~ Digital Number Figure 1. Digital number (0-255) distribution of first year sea ice. 5

11 150 potch2-seo_ice ( - 15 db) Digital Number Figure 2. Digital Number distribution of first year sea ice. 6

12 200 patch3- McMurdo " Q),_. ~ Digital Number Figure 3. Digital number (0-255) distribution over McMurdo Station. 7

13 300 patch4-ice (0 db) ;>, (.) 150 c: Q) :J c:r Q) )..j """' Digital Number Figure4. Digital Number distribution over glacial ice. 8

14 10 8 f.- patch5-land I I I I I ;:... u c: Q) :J 0' ~ 4!:Lo ~ - 2 f.- II~ I I I I Digital Number Figure 5. Digital number (0-255) distribution over bare rock. 9

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

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

17 Digital Number vs. Sigma Naught 10r ~------~ t I c 0> ::J cts z -20 cts E 0> Ci5 l r I Conversion equation: a 0 cm = 10 log (DN 2 )- K -50~----~~----~------~------~ L------~ Digital Number For a 0 = -15dB and DN = 40 (estimated from patch! and patch2), K = ~ -28 fl. 1.3 GHz, W Polnriznlion.otr {;;11111~1 MutllynJr tc 11 Thock F1rst Yoar leo Pressure R1dgol " Freahwater Lake a= ~... _ -~~~---~----~~--~~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