XXII ISPRS Congress 2012: Technical Commission VIII

Shortis, M.; Shimoda, H.; Cho, K.

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Multivolume work

Persistent identifier:: 1663813779

Title:: XXII ISPRS Congress 2012

Sub title:: Melbourne, Australia, 25 August-1 September 2012

Year of publication:: 2013

Place of publication:: Red Hook, NY

Publisher of the original:: Curran Associates, Inc.

Identifier (digital):: 1663813779

Language:: English

Additional Notes:: Kongress-Thema: Imaging a sustainable future

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Document type:: Multivolume work

Volume

Persistent identifier:: 1663822514

Title:: Technical Commission VIII

Scope:: 590 Seiten

Year of publication:: 2014

Place of publication:: Red Hook, NY

Publisher of the original:: Curran Associates, Inc.

Identifier (digital):: 1663822514

Illustration:: Illustrationen, Diagramme

Signature of the source:: ZS 312(39,B8)

Language:: English

Additional Notes:: Erscheinungsdatum des Originals ist ermittelt.; Literaturangaben

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: Shortis, M.; Shimoda, H.; Cho, K.

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2019

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [VIII/3: Atmosphere, Climate and Weather]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: GROUND-BASED CLOUD OBSERVATION FOR SATELLITE-BASED CLOUD DISCRIMINATION AND ITS VALIDATION M. Yamashita, M. Yoshimura

Document type:: Multivolume work

Structure type:: Chapter

In order to discriminate cloud and blue sky areas from the whole sky imageries, we use Sky Index (S7) and Brightness Index (BI) which are calculated from RGB channels of the image. SZ shows the blueness/greyscale and BJ shows the brightness in pixels. SI and BI are expressed by equation (1) and Q). DN; — DNp Sl = Br n (D DN5 + DNg DN, + DN , + DB Pr = 2 68 LR (2) @r—1) +3 where DN, ; digital number of Blue channel DN ; digital number of Green channel DN; ; digital number of Red channel n ; bit number of quantization level SI values have the range between —1.0 and 1.0. The blue sky area in the RGB image has the higher digital number in blue channel and the lower digital number in red channel. On the other hand, the clouds show white or grey on the image. Thus, the higher value of SI shows bluer sky, the value of near zero shows the clouds and the sun. B/ values are expressed by the range between 0 and 1.0. The bright pixels on the image show high BI. The pixels in the sun area have B/=1 and SZ =0. The whole sky areas consisted of the sun, clouds and blue sky are classified by the threshold curve which was derived from two dimensions of SI and BI coordinates. The threshold curve for sky area classification was determined by counting the frequency of SZ and BJ combination’s pixel. In this case, the threshold curve was used as BI = e°”“, When the coordinates plot under the threshold curve, these are classified as cloud area. The coordinates upper the curve are classified as blue sky area. The sun area in the imagery has the coordinates of S7 = 0 and BI = 1. In this way, the sky classified image was generated by SJ & BI threshold. Whole Sky Image (t) | Sky Index (SI) | | Brightness Index (BI) | | Masking for out of area | | Masking for out of area | z. A it in. DS zz Classifying Sun, Cloud, and Blue Counting the frequency of SI sky areas by SI&BI threshold and BI combination’s pixel | Determination of SI&BI threshold for dividing sun, / Sky classified image(t]/ cloud A areas Figure 1. The flowchart of cloud, blue sky and sun discrimination by whole sky imageries International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012 XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 3. OVERLAYING TO SATELLITE IMAGE As for the method of overlaying with cloud areas of both ground and satellite-based images, the cloud area on whole sky image are projected to ground surface plane with map coordinate. Our used fisheye lens has equidistant projection. In case of setting the ADFC fixed to north direction and levelled horizontally, the central pixel of whole sky (hemisphere) image corresponds to the zenith. According to equidistant projection, the distance from the image centre is in proportion to zenith angle shown in equation (3). deg 9 R ^ 90 e where — d,4; distance from zenith (image centre) R; Radius of whole sky image area (pixels) 6 ; Zenith angle (degrees) Consequently, the zenith (0) and azimuth (d) angles on whole sky image are able to calculate from the image coordinates (u, v). And then, the horizontal distance (HD) from the ground- based observation point, that is central position of whole sky image, to the target cloud can be estimated by given the approximate cloud height supposed from each cloud type, and the cloud areas on whole sky image are projected to map coordinates (x, y) using 6, gand HD. In these calculation and conversion, any distortions of fisheye lens and the curvature of ground surface are left out of considerations. 3.1 Calculation of zenith and azimuth angles Calculation of zenith and azimuth angles at any hemisphere image coordinates can be shown in equation (4) and (5). EN TTA CER = (4) when 0 € 0 « 180, pn = cos it o =) @; = 180 — cos ( R x 8; (5) when 180 < 0<360, Vi-—uv 90 @; = 180 * cos! ( > : x 3) where u;, v; ; Image coordinates of column and row (pixels) u,, v, ; Image centre coordinates (pixels) 0. ; Zenith angle (degrees) at (uj vj) @; ; Azimuth angle (degrees) at (u;, v;) In this study, the image size of hemispherical area has 1650 pixels and 1650 lines. Therefore the radius of circle (R) is 825 pixels and the image centre coordinate (u,, v,) is (824, 824) in case of the image upper left coordinates as (0, 0). 3.2 Cloud area conversion to map coordinates For each pixel classified as cloud area on whole sky image, the projected cloud area on the ground can be converted to map Intern coordinates any cloud I stratocumul of cumulus, The conver whole sky equation (6 where OC MOM NO ~~ As one of ( several wl synchrono Kyoto, Ja located at we use UT Figure 2 si whole sky Figure 2. Cloud dis image. ]

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