COLOR-INFRARED KITE AERIAL PHOTOGRAPHY: TAKE THREE

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1 COLOR-INFRARED KITE AERIAL PHOTOGRAPHY: TAKE THREE James S. Aber, 1 Susan W. Aber, and Toshiro Nagasako 2 1. Earth Science, Emporia State University, aberjim99@aim.com 2. Faculty of Education, Kagoshima University, Japan Color-infrared (CIR) photography was introduced during World War II for camouflage detection (Finney 2007). Since then, CIR aerial and space photography has been utilized often for many scientific and environmental applications. Such images include green, red, and near-infrared (G/R/NIR) bands portrayed in false color as blue, green and red respectively; active vegetation appears as red, pink and maroon. Take I: Dual-camera rig for kite aerial photography, shown here in a vertical position. Two analog (film) SLR cameras are mounted bottom to bottom for simultaneous pictures of the same scene in color-visible and colorinfrared formats. Camera position is fixed prior to flight and cannot be altered during flight. Total weight of this rig and cameras is 1.5 kg. Rig built by B. Leffler (1999). Take II: Tetracam ADC digital, colorinfrared camera in a remotely operated radio-controlled rig for kite aerial photography. R - radio receiver, P - pan servo and gears, B - NiMH battery pack, A - antenna mast, S - shutter miniservo, and T - tilt servo. Total weight of the camera, rig, and batteries is just over 1 kg. Camera rig built by JSA with parts provided by B. Leffler (2008).

2 We began developing methods for low-height CIR photography from kite platforms in 1999 based on analog (film) single-lens-reflex (SLR) cameras. By the beginning of this century, we had determined filters and camera settings for routine CIR kite aerial photography (KAP). However, CIR film became increasingly expensive, and many photo labs stopped developing this type of film. Our last use of CIR film took place in Take I: Color-visible (A) and color-infrared (B) kite aerial photographs of the campus of Emporia State University, Kansas. A portion of the football field, dormitory buildings, parking lots, automobiles, grass, and deciduous trees. Photosynthetically active vegetation is depicted in red and pink colors in the CIR image. Note variations in tree appearance in the color-infrared version. Kite photos taken with a pair of analog SLR cameras. Aber et al. (2001). Starting in 2008, we experimented with the Tetracam ADC digital CIR camera. However, this camera proved impractical for several reasons and was utilized only a few times with generally disappointing results. Take II: Color-visible (A) and Tetracam ADC color-infrared (B) digital images of the Nature Conservancy marsh complex, Cheyenne Bottoms, central Kansas. Active vegetation appears in bright red-pink colors in the latter. Kite aerial photographs from Aber et al. (2009).

3 Our third attempt for CIR kite aerial photography began last year based on a compact, digital, mirrorless SLR camera (Sony α6000) that was customized for B/G/NIR imagery (Arrow 2016). After several field trials for adjusting the camera settings and radio-controlled KAP rig, this camera produced excellent CIR imagery with sharp, clear pictures and high spatial resolution (~2 cm). Take III: Kite aerial photography rig for a Sony α6000 mirrorless DSLR camera with interchangeable lens and UV-haze filter. The shutter is triggered by an infrared LED mounted on an aluminum post in front of the camera s IR sensor (*). Camera body measures ~6½ by 12 cm; sensor is 24 megapixels; specially modified for B/G/NIR imagery. For SFAP use, the ISO setting is raised to 1600 to achieve fast shutter speed and sharp shots. Total weight of mount, camera and batteries is ~0.85 kg. Rig built by JSA (2017); rig kit from brooxes.com; infrared shutter trigger by J. Gentles. Take III: Normal color (left) and color-infrared (right) views of a pond surrounded by various types of active vegetation. In color-infrared, grass and deciduous trees are bright orange, conifers are dark orange, and water is dark blue. Kite photographs taken with specially modified Sony α6000 mirrorless DSLR cameras. Emporia, Kansas (2017).

4 In this false-color format, active vegetation appears in shades of orange. The hot spot, sun glint, and other special lighting effects are emphasized. A normalized-difference vegetation index (NDVI) could be extracted just as with conventional G/R/NIR color-infrared imagery. A final field test and demonstration was conducted at the Kansas Academy of Science fall field trip in Special lighting effects often seen in kite aerial photographs. Left: hot spot is the bright spot on the ground in direct alignment with the camera and sun. Right: sun glint from water surface, much like a mirror reflection. Sony α6000 mirrorless DSLR camera, eastern Kansas (2017). Overview (left) and closer shot (right) of Gladfelter Pond at the Ross Natural History Reservation of Emporia State University. Taken during the Kansas Academy of Science fall field trip, October 7, Selected references Aber, J.S., Aber, S.W., Buster, L., Jensen, W.E. and Sleezer, R.O Challenge of infrared kite aerial photography: A digital update. Kansas Academy of Science, Transactions 112, p Aber, J.S., Aber, S.W. and Leffler, B Challenge of infrared kite aerial photography. Kansas Academy of Science, Transactions 104, p Arrow Vegetation analysis sensors. Arrow Consulting. Accessed online < March 2018.

5 Typical spectral response for emergent, green vegetation. Blue (b) and red (r) light are absorbed in photosynthetically active leaves. Green (g) is reflected weakly, and near-infrared (NIR) is reflected strongly. Adapted from Clark et al. (2003). Typical response curves for CCD and CMOS image sensors without nearinfrared (NIR) blocking filters, showing the transmission response after light passes through the mosaic color filter over the image sensors. Adapted from Prosilica (2009). Conventional color-infrared photography (analog and digital) utilizes the green, red, and NIR bands, which are portrayed in false-color format as blue, green and red. Blue light is excluded by use of a yellow filter. In some cases, orange or red filters are used to further reduce visible light from reaching the film or sensor. In such G/R/NIR imagery, active vegetation appears in red, pink, and maroon colors. The Sony α6000 mirrorless DSLR camera is modified to record blue, green and NIR bands, which are portrayed in false-color format as blue, green and red. Red light is not recorded. In such B/G/NIR imagery, active vegetation appears in shades of orange. False-color combinations for G/R/NIR and B/G/NIR color-infrared imagery and the typical appearances of active vegetation and clear water bodies.

6 Color-infrared images from Emporia, Kansas. Above Riverside School in foreground and BNSF Railroad in background. Below Cottonwood River and floodplain. Spring 2017; Sony α6000 mirrorless DSLR camera.

7 Full references Aber, J.S., Aber, S.W., Buster, L., Jensen, W.E. and Sleezer, R.O Challenge of infrared kite aerial photography: A digital update. Kansas Academy of Science, Transactions 112, p Aber, J.S., Aber, S.W. and Leffler, B Challenge of infrared kite aerial photography. Kansas Academy of Science, Transactions 104, p Arrow Vegetation analysis sensors. Arrow Consulting. Accessed online < September Clark, R.N., Swayze, G.A., Livo, K.E., Kokaly, R.F., Sutley, S.J., Dalton, J.B., McDougal, R.R. and Gent, C.A Imaging spectroscopy: Earth and planetary remote sensing with the USGS Tetracorder and expert systems. U.S. Geological Survey, Spectroscopy Lab. Accessed online < speclab.cr.usgs.gov/papers/tetracorder/> August Finney, A Infrared photography. In Peres, M.R. (ed.), Focal encyclopedia of photography. 4th edition. Elsevier, Amsterdam, p Prosilica Prosilica cameras go airborne. Prosilica Camera News 11, May 2009, p. 2-4.