MultiCam A Multi-Spectral Imager for Airborne, Laboratory and Field Applications Instruction Manual

Transcription

1 MultiCam A Multi-Spectral Imager for Airborne, Laboratory and Field Applications Instruction Manual January 2008 Version 10

2 MULTICAM SPECIFICATION SHEET Features # of cameras up to 5 Imaging multi-spectral Boresight adjustment azimuth, elevation, rotation Lenses Interchangeable, F or C mount Spectral bands user selected Image capture synchronized (all cameras) Frame rate (max) 70 fps for 5 cameras (USB limited) Gain, offset, exposure Each camera separately set Auxiliary equipment GPS, AHRS (optional) Detectors Detector resolution, pixel size 1, , 12 µm Detector type CMOS Detector diagonal 1967 mm Exposure control TrueSNAP (electronic shutter) Max frame rate 500 fps (CMOS alone) Resolution 10 bits CMOS type Monochrome Bandpass filters Position between optics and CMOS Allocated volume (up to) 4mm 508mm 508mm Filter holders custom Software Camera control via USB (live preview, data capture, camera setting) GPS / AHRS data capture and time synch to imagery Camera alignment / boresighting Image co-registration Radiometric calibration Mechanical QuadCam PentaCam Length 270 mm / 106 in 328 mm / 129 in Width 210 mm / 83 in 333 mm / 131 in Height 212 mm / 83 in 254 mm / 100 in Mass (no lenses) 59 kg 86 kg Sensor mount Side or down looking Electrical Supply voltage 5 VDC Max current 5 Amps Supply location External Image transfer USB

3 Table of Contents Section Page 1 Hardware 1 11 Hardware Mounting 1 12 Camera Alignment Hardware 2 13 External Connections 3 14 Optics 3 2 Bandpass Filters 4 3 Driver Installation 7 4 Software 9 41 Section 1 - Image Display Section 2 - Video Controls Sections 3 and 5 - GPS / AHRS Control and Display Section 4 - Live View Controls Section 6 - Zoom Control Section 7 - Additional Menus File Menu Settings Menu Alignment / Boresighting 16 5 Frame Rate Study 19 6 Files and Headers GPS and AHRS Files Image Files 19 7 Radiometric Calibration Camera Gain Linearity 23 8 Camera Settings for Airborne Imaging 24 9 Modulation Transfer Function ENVI Software Co-registration Software Radiometric Calibration Software Installing the Software on Additional Computers 30

4 List of Figures Figure Page 1 System components: (a) PentaCam and (b) QuadCam 1 2 MultiCam mounting provisions: (a) PentaCam and (b) QuadCam 2 3 Alignment hardware: (a) shown with image sensor and (b) 2D CAD rendering of tip-tilt screw 2 4 External connections: (a) PentaCam and (b) QuadCam 3 5 C-style mounting provisions: (a) PentaCam and (b) a single MultiCam sensor 3 6 Imaging sensor with filter cover 4 7 Filter holder 5 8 Top cover / side removal: (a) PentaCam and (b) QuadCam 5 9 QuadCam oriented for filter displacement (a) and filter cover removal (b) 6 10 Set screw loosening (a) and filter holder removal with tweezers (b) 6 11 Initial driver installation pop-up 7 12 Second driver installation pop-up 7 13 Third driver installation pop-up 8 14 Fourth driver installation pop-up 8 15 Fifth driver installation pop-up 9 16 Sixth driver installation pop-up 9 17 Graphical user interface (PentaCam) Video controls GPS / AHRS: (a) controls and (b) display Crossbow AHRS (a) and Garmin GPSMAP76 (b) Live view: (a) controls, (b) schematic (for PentaCam), and (c) Sync Time button File menu selection Settings menu selection Camera Settings pop-up (PentaCam) Gain / Offset pop-up (PentaCam) Set Directory pop-up Alignment pop-up (PentaCam) Adjustment tool and hardware Crosshair on alignment target Irradiance calculation with bandpass filter Calibration using a calibrated irradiance lamp Calibration data Normalized response vs camera gain QuadCam on ENVI toolbar Reference cube pop-up RGB co-registration image Exposure time and f/# inputs DN pop-up Gain image file selection pop-up Dark field file selection pop-up Image cube save pop-up 30

5 List of Tables Table Page 1 Component description 1 2 Fujinon CF35HA - 1 specifications 4 3 Dimensions allocated for bandpass filter 3 4 Video capture controls 11 5 GPS / AHRS controls and display 11 6 Live view controls 13 7 Digital zoom controls 13 8 Camera Settings controls 14 9 Gain / Offset controls Alignment / boresighting controls Frame rate study Calibration camera settings Suggested starting point camera settings for airborne imaging MultiCam s MTF results Contents of radiance cube header file 30

6 1 HARDWARE While it is not necessary to have a comprehensive understanding of the MultiCam hardware in order to collect data, a low-level understanding of the components will help the user better understand how the system operates The items seen in Figure 1 represent the main components of the MultiCam system A description of each of these components is found in Table 1 Sensor Housing Alignment Screw USB Hub USB Connection Power Connection USB Hub USB Connection Power Connection Filter Cover Mounting Hardware Component USB Hub USB Connection Power Connection Filter Cover Alignment Screw Sensor Housing Mounting Hardware 11 Hardware mounting Filter Cover Mounting Hardware Sensor Housing (a) (b) Figure 1 System components: (a) PentaCam and (b) QuadCam Alignment Screw Table 1 Component description Function Converts one USB signal into multiple signals and vice-versa Connection used for camera communication with the USB hub Connection used to provide 5VDC to the image sensors Provides access to bandpass filter Used to point the sensor housing Contains a CMOS imaging array Means of fixturing MultiCam MultiCam has been designed so that it can be mounted on its side or from the bottom The side and bottom mounting provisions, shown in Figure 2, allow data to be collected in either the horizontal or vertical directions 1

7 ¼ through holes breadboard mounting ¼ - 20 holes for tripod mount ¼ - 20 Tapped Hole ¼ - 20 Through Holes (3 on Center) (a) (b) Figure 2 MultiCam mounting provisions: (a) PentaCam and (b) QuadCam As seen Figure 2, the mounting hardware provides both ¼ - 20 tapped and through holes Specifically, the bolt pattern has been machined so the unit can attached to standard optical breadboards or a tripod 12 Camera alignment hardware Each CMOS sensor has been equipped with a three degree-of-freedom (DOF) fixture allowing it to be accurately aligned Specifically, each sensor can be rotated, tipped, and tilted via the special mounting screws shown in Figure 3 Rotation Fixture Tip - Tilt Screw 1 Adjustment nipple 2 Keyed nipple adjuster 3 Holding screw 4 Adjustment plate 5 Base plate (a) (b) Figure 3 Alignment hardware: (a) shown with image sensor and (b) 2D CAD rendering of a tip-tilt screw 2

8 The rotation fixture labeled in Figure 3 allows the imaging sensor to rotate about the center of its CMOS array (ie, the optical axis) This rotation gives the user the ability to orient each sensor so the images returned are square each other The tip-tilt screws seen in Figure 3 provide camera pointing These special screws work by using a threaded nipple (1) to manipulate the separation between the adjustment and base plates Using three tip-tilt screws together allows the user to change the azimuth and elevation angles of each sensor After alignment, the position of each sensor is locked in place with a cap screw (3) A thorough description of the alignment procedure is found in Section External connections Only two connections are needed to operate the MultiCam hardware A single USB connection is needed for transferring image data, while +5 VDC is needed to power the image sensors and supporting electronics The external connections are shown in Figure 4 USB +5VDC USB +5VDC 14 Optics (a) (b) Figure 4 External connections: (a) PentaCam and (b) QuadCam Each of MultiCam s imaging sensors has a provision for C-mount fore optics The C-style mounting provisions are shown in Figure 5 C mount thread C mount thread (a) (b) Figure 5 C-style mounting provisions: (a) PentaCam and (b) a single MultiCam sensor 3

9 While C-style lens mounts have been chosen for MultiCam s sensors, adapters can be purchased allowing for the use of F-mount lenses MultiCam s 13 megapixel ( ) CMOS arrays require a lens capable of producing a 1967 mm image circle Therefore, F-mount and large format C-mount lenses are needed to prevent image degradation due to vignetting Typically, 1 format Fujinon lenses, with 35 mm focal length, have been shipped with the MultiCam hardware The mechanical specifications of these lenses are listed in Table 2 2 BANDPASS FILTERS Table 2 Fujinon CF35HA - 1 specifications Feature Specified Value Iris Range f14 - f22 Mass 180 g Diameter 51 mm Length 485 (at ) Mount C In each MultiCam sensor housing, a bandpass filter can be inserted in between the fore optics and the CMOS array This feature eliminates the need to purchase a new filter each time a lens change is desired The filter cover, which is labeled in Figure 6, covers the volume allocated for the filter assembly The dimensions of the filter volume are listed in Table 3 Figure 6 Imaging sensor with filter cover Filter Cover 4

10 Table 3 Dimensions allocated for the bandpass filter Dimension Value Height 4 mm Width 508 mm Length 508 mm Commercial off the shelf (COTS) filters of many different sizes can be inserted into the filter volume by machining custom filter holders Four filter holders that accommodate 25 mm diameter filters are shipped with each MultiCam system One such filter holder is shown in Figure 7 Bandpass filter, Ø= 25mm Set Screw Figure 7 Filter holder Removal and installation of the bandpass filters into the MultiCam hardware is very straightforward First, remove the top cover (PentaCam) or the sides (QuadCam) Figure 8 Top cover / side removal: (a) PentaCam and (b) QuadCam 5

11 Next, flip the system over so that it is oriented as shown in Figure 9a Now the filter cover can be removed as shown in Figure 9b 0 80 Screw (a) (b) Figure 9 QuadCam oriented for filter replacement (a) and filter cover removal (b) Loosening the two set screws, which are used to secure the filter holder, is the next step in the filter replacement process This step is shown in Figure 10a Tweezers (a) (b) Figure 10 Set screw loosening (a) and filter holder removal with tweezers (b) The final step, which is illustrated in Figure 10b, involves removing the filter holder It is important to note the orientation of the filter holder as it is removed from the sensor body Orientation is critical because the holder is not symmetrical about the center hole With the filter holder removed, a new filter can be inserted and secured with the holder s set screw (see Figure 7) After changing the filter, the filter assembly should be repositioned inside the camera body and secured It is important make sure that the set screws used to secure the filter holder in place are securely tightened because these screws also aid in holding the lens in position 6

12 3 DRIVER INSTALLATION If it is necessary to install the sensor drivers, a pop-up window will be displayed after the system is connected via USB The initial pop-up screen is shown in Figure 11 As seen, the bottom radio button, which is labeled No, not this time, should be selected Figure 11 Initial driver installation pop-up After selecting the Next button, the screen shown in Figure 12 appears Select, Install from a specific location (Advanced) Z Figure 12 Second driver installation pop-up In the next pop-up, which is shown in Figure 13, the second option should be selected Specifically, choose Include this location in the search: and Browse to C:\MultiCam\ 7

13 A MultiCam Instruction Manual Version 10 Figure 13 Third driver installation pop-up Figure 14 shows the fourth driver installation pop-up screen On this screen, select the top option and hit Next Figure 14 Fourth driver installation pop-up Select Continue Anyway when the fifth pop-up appears 8

14 Figure 15 Fifth driver installation pop-up The final pop-up is shown in Figure 16 On this screen, select Browse, then point to C:\Multi- Cam select ezusbsys, and press OK This completes the driver installation Figure 16 Sixth driver installation pop-up 4 SOFTWARE The Graphical User Interface (GUI) used to control the MultiCam system is shown in Figure 17 Notice that the GUI has been divided into seven sections Each of these sections is described below in detail 9

15 41 Section 1 - Image display Figure 17 Graphical user interface (PentaCam) The image window, labeled 1 in Figure 17, is used to display data collected by the imaging sensors Specifically, one to five (for PentaCam) images can be displayed depending on the user s preference 42 Section 2 - Video controls The video capture controls are shown in Figure 18 A description of each control is found in Table 4 Figure 18 Video controls 10

16 Control Label Live Capture Live Capture Stop Table 4 Video capture controls Control Type Description When checked, the image display is updated during image Check box capture Live image display during image capture will decrease the rate at which frames are saved to disk Button Initiates live image display without saving to disk Button Initiates the saving of image data to disk Button Stops live image display and /or data capture 43 Sections 3 and 5 - GPS/AHRS control and display Sections 3 and 5 of the GUI contain the controls and display needed for GPS and AHRS data capture In order to activate these features, the user must request the system to search for GPS and AHRS devices upon startup This procedure is described in greater detail in Section 462 Figure 19 displays the GPS / AHRS controls and display Table 5 describes the contents of Figure 19 in detail Label AHRS Log GPS Log Capture Stop Roll Pitch Yaw Lon Lat Alt (a) (b) Figure 19 GPS / AHRS: (a) controls and (b) display Table 5 GPS / AHRS controls and display Type Description Check box When checked, a data file containing AHRS data will be created in the root directory Check box When checked, a data file containing GPS data will be created in the root directory Button control Initiates GPS and /or AHRS data capture Button control Stops GPS and /or AHRS data capture Numeric Display Displays roll data during AHRS data capture Numeric Display Displays pitch data during AHRS data capture Numeric Display Displays yaw data during AHRS data capture Numeric Display Displays longitude data during GPS data capture Numeric Display Displays latitude data during GPS data capture Numeric Display Displays altitude data during GPS data capture The MultiCam software is configured to work with the AHRS400 made by Crossbow (wwwxbowcom) Because different inertial systems have different packet protocols and serial commands, the MultiCam software does not support other INS devices An image of the AHRS400 is seen in Figure 20a 11

17 (a) (b) Figure 20 Crossbow AHRS (a) and Garmin GPSMAP76 (b) The GPS system used during software testing was the GARMIN GPSMAP76, seen in Figure 20b However, the GPSMAP76 produces standard NMEA packets via RS-232 Therefore, other GPS systems that comply to this protocol should work with the PentaCam software 44 Section 4 - Live view controls Section 4 contains controls used to select which cameras will be displayed when the Live button (see Figure 18) is pressed In addition, Section 4 contains a schematic to help the user determine the physical position of each sensor and a Sync Time button used to synchronize the Windows clock with the incoming GPS signal (when GPS is active) Figure 21 shows the controls and the PentaCam schematic Table 6 describes each in more detail (a) (b) (c) Figure 21 Live view: (a) controls, (b) schematic (for PentaCam), and (c) Sync Time button 12

18 Label Cam1 Cam2 Cam3 Cam4 Cam5* Camera View Sync Time Type Check box Check box Check box Check box Check box Image Button *PentaCam only Table 6 Live view controls Description When checked, data captured by Cam1 is displayed during live preview When checked, data captured by Cam2 is displayed during live preview When checked, data captured by Cam3 is displayed during live preview When checked, data captured by Cam4 is displayed during live preview When checked, data captured by Cam5 is displayed during live preview Used to provide the user with a reference location for each of the cameras The numbers shown indicate the position of each sensor relative to the USB and power inputs Used to (re)synchronize the Windows clock with GPS time Note that the Windows clock is automatically synchronized at software start up when a GPS signal is present 45 Section 6 - Zoom control Section 6 contains the controls used to manipulate the display s digital zoom It should be noted, however, that the digital zoom buttons are only active when a single camera is selected for live viewing or alignment The digital zoom controls are shown and described in Table 7 Image Control Type Button Button Button Button 46 Section 7 - Additional menus Table 7 Digital zoom controls Description Increases the display s digital zoom Decreases the display s digital zoom Eliminates all digital zoom and decimation When pressed, a control box appears in the upper right-hand corner of the display window This control box can be dragged with the mouse to change the region of the image displayed in the preview window Section 7 contains menu controls used to set the root directory, change camera settings, and perform camera alignment The contents of each menu is described below 461 File menu When the File menu is selected, as shown in Figure 22, the user is given the option to exit the program 13

19 462 Settings menu Figure 22 File menu selection Several options are available when the Settings menu is selected These options are shown in Figure 23 Figure 23 Settings menu selection When Camera Settings is selected, a pop-up screen appears This pop-up screen, which is shown in Figure 24, allows the user to control various aspects of image capture and display Details associated with these controls are listed in Table 8 blue green red IR1 IR2 Label Exposure Time Cam Capture Cam Name Control Type Numeric String Figure 24 Camera Settings pop-up (PentaCam) Check box Table 8 Camera Setting controls Description Time, from 1 to 321 ms, that each sensor integrates When checked, image data is saved after the Capture button (Figure 18) is pressed Allows the user to enter a name for each camera (this name appears in Section 4 of the GUI) 14

20 Use GPS GPS Baud Rate OK Cancel Label Capture Frames Use AHRS Set As Default Go to Default Control Type Numeric Check box Check box List Box Button Button Button Button Description Determines the number of frames saved to disk after the Capture button (Figure 18) is pressed When checked, the MultiCam software will look for a AHRS device during startup When checked, the MultiCam software will look for a GPS device during startup Used to select the baud rate of an incoming GPS signal Implements the current settings Removes the Camera Settings pop-up from the screen without implementing the current settings Saves the current camera settings as default Changes the current camera settings to the default camera settings The second option located on the Settings menu brings up the gain and offset controls These controls are shown in Figure 25 and described in Table 9 Gain Label Figure 25 Gain / Offset pop-up (PentaCam) Table 9 Gain / Offset controls Control Type Description Slider / Txt Box Number, between 0 and 3300, used to set the sensor gain (Note: high number is actually lower gain) 15

21 Offset OK Label Cancel Set As Default Go To Default Control Type Slider / Txt Box Button Button Button Button Description Number, between and 3300, used to set the sensor offset Implements the current settings Removes the Gain / Offset pop-up from the screen without implementing the current settings Saves the current settings as default Changes the current settings to the default settings The final option on the Settings menu is Set Directory When this option is selected the pop-up in Figure 26 appears Figure 26 Set Directory pop-up The Set Directory pop-up allows the user to select the folder in which captured data files (GPS, AHRS, image) are saved 463 Alignment / boresighting As discussed in Section 12, the MultiCam sensors have special alignment screws that allow the azimuth and elevation angles of each sensor to be manipulated Alignment is achieved when each lens is oriented so that it is parallel with the other lenses When the lenses are parallel to each other, the difference between each sensor s field of view is minimized (when the lenses are focused to near infinity) 16

22 There is no immediate need to modify the alignment when the system is received (the system is aligned before shipment) However, all of the hardware and software tools needed for alignment are available if alignment becomes necessary Camera alignment begins by removing the cover of the MultiCam system (see Figure 8) Next, use the Alignment menu to open up the pop-up seen in Figure 27 The contents of the Alignment pop-up are described in Table 10 Label Ref Camera Align Camera Subtraction Summation Ref Cam Align Cam Center Cross Apply Stop Figure 27 Alignment pop-up (PentaCam) Table 10 Alignment / boresighting controls Control Type Description Radio button Controls which sensor is the reference sensor Radio button Controls which sensor is the align sensor Radio button Initiates a routine where the Align Camera image is subtracted from the Ref Camera image Radio button Initiates a routine where the Align Camera image is added to the Ref Camera image Radio button Displays the Ref Camera image Radio button Displays the Align Camera image Check box Overlays a crosshair on the center pixels of the displayed image Button Applies the current settings Button Stops live image display 17

23 Adjustment of the alignment screws is done with a special tool This tool is used to manipulate the hardware described in Figure 3 The tool, along with the alignment hardware, is shown is Figure 28 Figure 28 Adjustment tool and hardware In order to achieve parallel lens orientation, an alignment target is placed at a distance and the tip-tilt screws are adjusted until the center crosshair is on top of its target This process is shown in Figure 29 A Figure 29 Crosshair on alignment target 18

24 The alignment target shown in Figure 29 is simply a true-scale print out of MultiCam s base A copy of the alignment target has been shipped with the system Alignment is achieved when each sensor s center crosshair is overlayed on its target The software s digital zoom capabilities should be used increase the ability to achieve true alignment 5 FRAME RATE STUDY The maximum frame rate of the MultiCam system, shown in Table 11, was determined by reducing the exposure time to 1ms and collecting 10 images per camera Therefore, the frame rate reported is the average frame rate during the capture of 10 images Note that the Live Capture check box (Figure 18) was disabled during this study # of Cameras FILES AND HEADERS Table 11 Frame rate study Integration Total Capture Images Time (ms) Duration (s) Captured Frames/sec When image, GPS, and AHRS data is captured, PentaCam s software creates data files and saves them in the folder selected from the Settings menu (Figure 26) Sections 61 and 62 describe the saved files 61 GPS and AHRS files GPS and AHRS data files are saved in the root directory as a text file The files are named using the start time, date, and file type For example, a GPS file captured on December 1, 2006 at 1:00 PM is given the following name: gpstxt GPS and AHRS files are space delimited Therefore, they are best viewed using a spreadsheet program 62 Image files When image data are captured, a header and an image file are created The header is a text file that contains information about camera settings and capture time Header files are named using the capture time, date, and camera number For example, a header captured on December 1, 2006 at 1:00 PM with camera 4 is given the following name: Camera4hdr

25 The second file created during image capture is the image data file This file has a fla extension and is saved in binary format The image file, combined with its header, is formatted to open using ENVI ( 7 RADIOMETRIC CALIBRATION Before shipment, each MultiCam sensor is radiometrically calibrated using a lamp of known irradiance Specifically, Equation 1 is used to calculate the gain needed to convert digital numbers (DNs) into radiometric units The calibration is valid for specific gain / offset settings of the camera DN = DF + G $ L $ Where DN is digital number, DF is dark field (in DN units), G is gain, ET is exposure time, f/# is the f-number of the fore optics, and L is irradiance at the entrance to the fore optics Units for L do not matter as long as they are consistent when performing the calibration and subsequently converting image data to radiance In general, the terms in the equation, DN, DF, G, and L are matrices represented as a 2D image The L matrix has the same value at all elements ET and f/# are scalars All these analyses can be performed as image analysis within ENVI In order to calculate the incident irradiance on the fore optics, the area under the lamp s irradiance curve is determined in the region bounded by a bandpass filter A graphical representation of the area calculation is shown in Figure 30, while the mathematical representation is seen in Equation 2 ET f/# 2 [1] 20

26 90 Irradiance Calculation Bandpass filter Calibration lamp transmission (%) irradiance (mw/m^2/nm) Irradiance Area wavelength (nm) Figure 30 Irradiance calculation with bandpass filter 0 L = FT $ L L $ =0 [2] In Equation 2, F T is the filter transmission, L L is the irradiance of the calibration lamp, and is the wavelength step size used for numerical integration Once a gain image, G, has been calculated using Equations 1 and 2 for some f/# and ET, the calibration equation can be generalized to account of any f/# and ET The general calibration equation is shown in Equation 3 (DF image should be captured under field conditions, since it depends on temperature) Where : DN = DF +(G $ f/# R 2 $ ET R $ L) f/# R = f/# 0 f/# n ET R = ET n ET 0 The subscript values in Equations 4 and 5 distinguish between the reference f/# and ET (given a value of 0) and the f/# and ET for measurement n Gain images, calculated using Equation 1, for each sensor (with its specific bandpass filter in place) have been shipped with the system (on the CD) The calibration f/# and exposure time (f/# 0 and ET 0 ) have already been accounted for in the gain images, and therefore, irradiance at 21 [3] [4] [5]

27 the entrance to the fore optics can be determined by plugging in the values for DN, DF, f/# n, and ET n into Equation 6 L = (DN DF) $ f/# n 2 G $ ET n [6] Section 92 describes an ENVI routine shipped with the system This routine should be used to convert raw images (DN units) to radiometric images (radiometric units) However, all of the calculations can be done in ENVI once the DN, DF, and G images are saved The gain, offset, and exposure settings used during calibration are listed in Table 12 An image of the setup used to collect the calibration data is shown in Figure 31 As seen, the illumination produced by the calibration lamp is reflected off spectralon before being collected by the fore optics Camera# Filter Blue Green Red IR1 IR2 Table 12 Calibration camera settings Camera Gain Camera Offset Exposure Time (ms) 1, , , , f/# Spectralon MultiCam Calibration Lamp Stray Light Shield Figure 31 Calibration setup using a calibrated irradiance lamp 22

28 Calibration Data Percent (%) Radiance (µw/cm^2/sr/nm) MV13 QE Sigma Lens Oriel Lamp Wavelength (nm) Figure 32 Calibration data The transmission of each bandpass filter, detector QE, lens transmission, and lamp radiance is shown in Figure 32 Note that the lens transmission has been normalized to a maximum transmission of 90% 71 Camera gain linearity In order to know if it is appropriate to apply (use in calibration) the gain images generated by the calibration at a single camera gain to other gain settings, it is import to understand how changes in camera gain affect the response (DNs) of the detector Figure 33 is a plot of relative response vs camera gain setting Notice that the response is not linear 23

29 Figure 33 Normalized response vs camera gain Because the camera s response to gain changes is not linear, a full characterization of each sensor should be completed in order to generalize the calibration equations for all camera gain settings Alternatively, a calibration could be completed for all camera settings used during data collection 8 CAMERA SETTINGS FOR AIRBORNE IMAGING A study was conducted in order to determine a reasonable set of camera parameters for airborne imaging These settings are not absolute but can be used as a starting point during aerial data capture Data were collected with each image sensor while looking at plant life illuminated by the sun The data were captured at f/28 in order to minimize the integration time needed to achieve adequate signal while using narrow bandpass filters Table 13 shows the camera parameters chosen Notice that the airborne image settings are identical to the settings used during calibration Table 13 Suggested starting point camera settings for airborne imaging Camera# Filter Camera Gain Camera Offset Exposure Time (ms) 1 Blue 1, Green 1, Red 1, IR1 3, * IR *PentaCam only f/#

30 9 MODULATION TRANSFER FUNCTION (MTF) The MTF for each sensor / filter / lens combination was calculated using Imatest software Imatest software is a commercially available package available at wwwimatestcom The Imatest software outputs MTF50, which is a numeric representation of perceived image sharpness Details regarding the setup used to collect the MTF, as well as, the mathematics behind the calculation are discussed in detail at: Table 14 summarizes the results of the MTF study carried out using the MultiCam system Table 14 MultiCam s MTF results Camera Filter MTF 50 Filter Lens # Model # (cycles/mm) 1 Blue OS Green OS Sigma 3 Red OS mm 4 IR1 OS * IR2 OS *PentaCam only Notice that the MTF50 is relatively constant when the blue, green, red, and IR1 filters are used However, there is a steep drop-off in the MTF50 for the IR filter This drop-off is most likely due to the poor lens performance in the IR region 10 ENVI SOFTWARE Two analysis software programs have been shipped with the MultiCam system The first program is used for image co-registration and the second program is used to apply gain images to convert raw images (DN units) to radiometric images (radiometric units) Before using the ENVI software, the folder named, MultiCam_sav must be put in the correct ENVI directory C:\RSI\IDLXX\products\enviXX\save_add Note that XX in the above address refers to a specific version number Once the folder is placed into the directory, a MultiCam option will appear on the main ENVI toolbar The updated MultiCam toolbar is shown in Figure 34 25

31 101 Co-registration software Create Calibration Co-registration Figure 34 QuadCam on ENVI toolbar The objective of the co-registration software is to spatially warp one or more images to match a reference image Warping reduces the spatial differences between images that have not been removed by hardware alignment, and correct for paraxial shift due to the displacement of the lenses However, parallax correction is best applied at infinity, and can not be applied to image with objects at different depth of field After Co-registration has been selected on the ENVI toolbar (Figure 34), the pop-up screen shown in Figure 35 appears Figure 35 Reference cube pop-up The pop-up shown in Figure 35 asks the user to select a reference file The reference file is a time series of images, ie, an image cube (fla extension) produced by a single sensor The 26

32 images in the reference cube are not warped by the co-registration software Instead, it is used as the master image to which all other images are matched After the reference cube has been selected, the software prompts the user to select up to three additional time-series for co-registration If less than five cameras (PentaCam) are desired the user can stop the analysis by selecting Cancel The co-registration, not only co-registers the time sequence of images, but also parses the timesequence and creates multispectral image cubes (of time-synchronized images) Therefore the output of the co-registration analysis is a series of image cubes (file extension cub ) saved in the same directory as the reference data file The total number of cubes is equal to the number of images in each input data file Each cube contains five (if all five PentaCam cameras are used) images which can be selected to form a RGB color image This process is further illustrated in Figure 36 Available Bands Output RGB Image Figure 36 RGB co-registration image Note that the co-registration procedure produces the best results when objects are viewed at large distances (ie ) This is due to the paraxial lens displacement 102 Radiometric calibration software The calibration software shipped with the system can be used to convert digital numbers to radiometric units The software applies Equation 7, which is simply Equation 3 solved for L L = DN DF G $ f/# R 2 $ ET R [7] Dimensional analysis of Equation 7 shows that L will have the same radiometric units as the source used to calculate the gain image (G) 27

33 The radiometric calibration software is started by selecting Create Calibration under the Penta or QuadCam heading on the ENVI toolbar (see Figure 34) Once started, the pop-up shown in Figure 37 appears asking the user to enter the exposure time and f/# of the image undergoing calibration Figure 37 Exposure time and f/# inputs The exposure time and f/# entered represent ET n and f/# n as described in Equations 4 and 5 Once the user has entered the appropriate exposure time and f/#, the software prompts the user to enter an image cube with units in DNs The pop-up used to facilitate this process is shown in Figure 38 Figure 38 DN pop-up Next, the software requires the user to input a gain image The gain image is generated by using a source of know radiance Gain images have been shipped with the system (on the CD) but it is good practice to recalibrate (calculate new gain images) on a regular basis or if any of the optical hardware changes (lens, filters, etc) The gain image pop-up is shown in Figure 39 28

34 Figure 39 Gain image file selection pop-up The final input required by the software is a dark field image The dark field should be collected using the same (camera) gain, offset, and exposure time as the DN image The dark field pop-up is shown in Figure 40 Figure 40 Dark field file selection pop-up After the dark field image is selected and the software calculates the radiance cubes, the user is asked to save the calibrated images using the pop-up seen in Figure 41 29

35 Figure 41 Image cube save pop-up Notice that the default file name for the radiance cube is derived from the current time, current date, camera name, and rad for radiance The default file extension is fla However, both the name and file extension can be changed by the user In addition to the radiance cube, the calibration software creates a header file (file extension hdr ) containing information about the radiance cube and the input images Table 15 lists the information contained in the header file created with the radiance cube Notice that the header contains information about the radiance data, as well as, the images used by the ENVI to create the radiance images Table 15 Contents of radiance cube header file Radiance Cube Lab Calibration Data Field Data (Flight Settings) creation date dark field file name camera name & number creation time dark field file location start & end capture times # of images (bands) camera gain, offset, & exposure time DN file name & location 11 INSTALLING THE SOFTWARE ON ADDITIONAL COMPUTERS The MultiCam software is fully installed and operational on the laptop shipped with the system However, it is possible to install the software on additional computers 30

36 Installing the software is straightforward The CD shipped with the system contains a folder called MultiCam Software The contents of this folder contain all of the necessary components needed to run the software, including the camera driver Therefore, all the user must do to use the software is copy the MultiCam Software folder to the C drive on the new computer After the software is copied and the system is connected via USB, the user must install the drivers using the process outline in Section 3 31