NRMT 2270, Photogrammetry/Remote Sensing

Lecture 7

Leica ADS 80 Camera System and

Imagery. Ontario ADS 80 FRI Imagery.

Tomislav Sapic GIS Technologist

Faculty of Natural Resources Management Lakehead University

Leica ADS-80 Camera System • The camera itself is part of a complex computer and navigation system.

1 - Sensor (Camera) Head with: • Digital Optics • IMU (Inertial

Measurement Unit) 2 – Control unit with a

position and attitude computer POS (Position and Orientation System).

3 – Mass Memory 4 – Operator interface 5 – Pilot guidance indicator 6 – Mount PAV80 (gyro

stabilized mount).

Source: Fricker (2001).

Two other systems are added to the aerial photo flight operation: • Flight and Sensor Control Management System (FCMS) • Attitude and Position Measurement System

Leica ADS-80 • Leica ADS (Airborne Digital Scanner) – made by Leica Geosystems. • The camera is part of a much larger onboard system. • Used in Ontario’s province-wide aerial imaging for the primary purpose of creating the enhanced forest resource inventory (eFRI).

• CCD lines having 12000 pixels (detectors) each.

• Detector (pixel) size: 6.5 μm

• Dynamic range CCD chain (radiometric

resolution): 16 bit

• Spectral bands (in nm)

o Panchromatic 465 – 676

o Red 604 – 664

o Green 533 – 587

o Blue 420 – 492

o Near-infrared 833 - 920

• Field of View (swath angle): 64⁰

Source: Leica Geosystems (2014).

Source: Leica Geosystems (2008)

Leica ADS-80 Camera Head

• The focal plane module consists of four CCD housings with linear arrays of pixels (detectors).

Source: http://www.fotointern.ch/archiv/2009/06/28/wie-heute-luftaufnahmen-entstehen-und-wozu-sie-dienen/

Source: http://www.agrosensing.com/aerea.html

Leica ADS-80 Gyro-stabilized unit Leica PAV80

Source: Leica Geosystems (2014a).

• Compensates angular aircraft movements

o Pitch -8° to +6° o Roll -7° to +7° o Drift within ± 30°

• This allows for taking true vertical imagery. • As a result, simplified aero triangulation.

Source: Sandau et al. (2000)

Leica ADS80 Control Unit (Camera Computer) Within the System

The control unit has high data throughput of 130 MB/sec

Stores all mission data – image, orientation and housekeeping data.

Leica ADS80 Control Unit CU80

Leica ADS40 Example

Leica ADS-80 Attitude and Position Measurement System

IMU measures and reports on a plane’s velocity, orientation and gravitational forces by the use of accelerometers and gyroscopes. Relative orientation and velocity from IMU and absolute position and velocity from GPS are used to correct low-frequency errors in the navigation solution.

POS generates both a real-time and post-processed position and orientation solution. POS has the ability to control automatically the

stabilised platform yaw, and to remove crab and drift.

Source: Sandau et al. (2000)

Leica ADS-80 Flight and Sensor Control Management System (FCMS)

Source: Sandau et al. (2000)

• FCMS controls, coordinates and monitors individual subsystems and provides a graphical user interface.

Flight Management • Different displays of suggested flight path, approach and turns for operator and pilot. • Keeps track of flown, not flown and lines that need to be re-flown (because of, e.g., clouds). • Vector data and ground control points as a backdrop for flight guidance. • Optimized guidance information for flight lines to be flown.

Navigation System GNSS (GPS) supported navigation – navigation and graphical guidance is displayed during all phases of the survey flight.

Sensor Control • Interfaces the hardware and allows for different parameters to be transferred to the hardware and status information read back. • Automatic sensor release – starts and stops the sensor according to the flight plan.

Flight & Error Data Log Data, e.g. flight track, start and stop of imaging sequences, sensor parameters, are stored for precise evaluation, optimization and maintenance.

Test & Service Facility Service technicians are able to locate and replace faulty parts or update internal software.

FCMS Interfaces

Leica ADS-80 Imagery • The pushbroom scanner takes seamless images from different angles (allowing for stereo viewing), creating separate scenes:

•The fact that each point is scanned three times, from three different angles, also helps in stabilizing the image geometry, since pushbroom scanned images have inherently poor geometry (each line represents an independent image!) (Mikhail et al. 2001).

RGB NIR

Leica ADS-80 Imagery

• ADS-80 CCD sensor contains several lines, i.e., the sensor can simultaneously take several seamless image strips.

• Image strips are taken at different angles to allow for stereo viewing.

• eFRI imagery is captured in R,G,B, NIR and at 16⁰ backward and at nadir, and in PAN at 14⁰ backward and at 2⁰ and 27⁰ forward.

• Each line has 12000 pixels (CCD detectors) along it.

• One pair of PAN lines are staggered laterally by 0.5 pixels, halving the RGB & NIR spatial resolution.

RGB NIR

PAN PAN

Nad

ir (0⁰)

PAN

Forw

ard 2

⁰

Leica ADS-80 Imagery

Source: Paternaki (2006).

There are several separate product levels created from the ADS-80 imagery:

Level 0: raw imagery (usually not delivered to the client).

o Contains significant distortion.

o Total overlap between image strips is critical in removing distortions.

Level 1: stereo image strips – georeferenced but not ortho-rectified.

o Derived from Level 0 imagery.

o Used for stereo-viewing.

Level 2: ortho-rectified imagery (can’t be seen in stereo).

o Derived from Level 1 imagery.

o Usually image tiles (e.g., 5 x 5 km).

o Used for capturing earth surface features (lakes, streams, roads, etc.) into GIS layers.

Digital Surface Model (DSM), points with surface elevations.

o Derived from Level 1 imagery through stereo (parallax based) measurements.

Classified DSM – points classified in vegetation (trees), water and ground.

Leica ADS-80 Imagery

Level 0

Level 1

Source: Paternaki (2006).

Source: Pateraki (2006).

Linear (Array) Digital Imagery vs. Frame (Area Array) Digital Imagery

• Less time needed to aerial triangulate (ortho-rectify, mosaic) linear than frame digital imagery.

Frame Digital Imagery

Linear Digital Imagery

• An example project showing how the entire camera system combined with the film-strip type of imagery results in a greatly reduced image post processing time. • Equivalent range, precision and accuracy of simple digital frame imagery would likely take weeks.

Source: Leica Geosystem (2008a).

FRI ADS Aerial Imagery in Ontario

• Ontario FRI based imagery has been flown with Leica ADS cameras and delivered to the MNR by North West Geomatics, based out of Alberta. • ADS data has been delivered for all forest management units (FMUs) in Ontario and it has, on average, a 1 m positional accuracy (LIO 2013).

FRI ADS Aerial Imagery in Ontario

Delivered ADS data:

o Three single band panchromatic image strips , 16 bit and a ground resolution of 20 cm at one backward (14⁰) and two forward (2⁰ and 27⁰) view angles.

o Two four-band multispectral (R, G, B, NIR) image strip, 16 bit and a ground resolution of 40 cm, at nadir and a backward (16⁰) view angle.

Leica Geosystems 2008

Level 1 (stereo imagery)

• 40 cm spatial resolution, orthorectified (planimetrically correct imagery -- true horizontal distances, such as on topographic maps), multispectral (RGB+NIR) 5x5 km tiles.

True Colour False Colour

Delivered ADS data:

FRI ADS Aerial Imagery in Ontario

Level 2

Use of ADS Aerial Imagery in Forest Management in Ontario

• Digital Surface Model (DSM) – 5 x 5 m elevation point grid derived and interpolated from the stereo imagery. • DSM represents the surface seen from above, not the terrain under (e.g., tree canopy). • Points are further attribute classified based on the orthorectified imagery into three classes: bare earth, deep water and vegetation.

Delivered ADS data:

Ontario eFRI ADS Camera Files

• ADS imagery products have been delivered as a set of files with some parts of the set having a complex construction of files and their relations.

• L 1 files are particularly complex, composite files, whose parts are dispersed over four different folders.

Ontario eFRI ADS Camera Files • The cam folder hosts camera calibration files, which contain geometric and radiometric calibrations for CCD lines (B, G, R, NIR at nadir and 16˚, and PAN at 14˚ and 2˚ .

L 1

12,000 x,y pairs., for each detector (pixel) position in the sensor line.

Ontario eFRI ADS Camera Files • The L1 folder contains index files (.ads) and strip segments in a .tif format. L 1

Ontario eFRI ADS Camera Files

• The odf folder contains: o Orientation data files (.odf) that contain exterior orientation

parameters for each scanned line. o Orientation data files after bundle adjustment (.adj).

L 1

Ontario eFRI ADS Camera Files L 1

• The sup folder contains ‘socket support file format’ (.sup) files and pyramid (.rrd) files. • .rrd, pyramid files, contain

multiple raster layers at increasingly coarser spatial resolution, which are displayed when zoomed out of the image, to speed up the display.

• .sup files contain references to file locations, including .odf, .adj, and .cam fiels, and can be opened in a text editor.

Pyramid, .rrd, files can enlarge the size of image files by up to 40%!

Ontario eFRI ADS Camera Files

L 2 • L2 NRGB, 5x5 km tiles with auxiliary files.

• OBM derived tile number.

Ontario eFRI ADS Camera Files

DSM • DSM text file.

• GIS (shapefile) file generated from the DSM text file.

FRI ADS Aerial Imagery in Ontario

• Area of Undertaking (all FMUs together) covers 43.8 M ha. • The spatial resolution (GSD) of the imagery plus the radiometric resolution plus the multi layered imagery, has created an enormous amount of data - ~360 TB for the entire Area of Undertaking. • All data are available to Lakehead students, either through Ontario Scholars GeoPortal (ortho imagery), or by ordering the imagery through the Lakehead Library.

1

2

1

3

2

3

Use of ADS Aerial Imagery in Forest Management in Ontario

Digital Surface Model

• A small sample inspection showed that DSM represents well continuous surfaces but not as well sudden drops in heights, such as the case with buildings and e.g., forest canopy. The DSM drop is gradual -- over a 15 m distance away from the edge for objects 18 – 20 m high (Lusignan 2011)

FRI ADS Imagery Advantages and Potentials

• Higher spatial resolution than previous aerial FRI imagery, and availability of the NIR band should lead to higher accuracy of the FRI, the dataset that traditionally has had low accuracy.

• Already the imagery is yielding a much more accurate and precise classification and digitization of basic features such as lakes and roads. • The high accuracy DSM layer is expected to lead to higher accuracy in tree height estimates.

References:

Fricker P. 2001. ADS40 – Progress in digital aerial data collection. Photogrammetric Week 01, Institute of Photogrammetry. Heidelberg, Germany.

Gehrke, S., Morin, K., Downey, M., Boehrer, N., and Fuchs, T. 2010. Semi-global matching: An alternative to LIDAR for DSM generation. In Proceedings of the 2010 Canadian Geomatics Conference and Symposium of Commission I.

Leica Geosystems. 2008. Leica Geosystems Digital Airborne Solutions.

Leica Geosystems. 2008a. Leica - 3rd Generation Airborne Digital Sensors: Features/Benefits for Remote Sensing & Environmental Application. http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCoQFjAA&url=http%3A%2F%2Fmars.jrc.ec.europa.eu%2Fmars%2Fcontent%2Fdownload%2F1176%2F6943%2Ffile%2FT1_Rohrbach_Rohrbach-AirborneSensors-3rd_Leica.pdf&ei=35NkUvrqMa-E2gWWqoCwBw&usg=AFQjCNFxEdk3vWVOSM_CAXFELGDLjceZNg&bvm=bv.54934254,d.b2I&cad=rja. October 10, 2013.

Leica Geosystems. 2014. Leica GeosystemsLeica ADS80 Product Specification. http://www.leica-geosystems.com/downloads123/zz/airborne/ads80/brochures-datasheet/ADS80_datasheet_en.pdf . Viewed February 2014.

Leica Geosystems. 2014a. Product Description Leica PAV80. http://www.leica-geosystems.com/downloads123/zz/airborne/PAV80/documentations/Leica_PAV80_Product_Description.pdf. Viewed February 2014.

LIO (Land Information Ontario). 2013. Forest Resource Inventory Digital Aerial Imagery Metadata. https://www.appliometadata.lrc.gov.on.ca/geonetwork/srv/en/main.home. November 1, 2013.

Lusignan E. 2011. Ontario eFRI's digital surface model: characteristics and uses in forest management related measurements and visualizations. Undergraduate thesis. Lakehead University.

Mikhail, E. M., J. S. Bethel, and J. C. McGlone. 2001. Introduction to Modern Photogrammetry. John Wiley & Sons, INC.

Pateraki, M. 2006. Digital Aerial Cameras. International Summer School “Digital Recording and 3D Modelling”. Crete, Greece.

Sandau, R., B. Braunecker, H. Driescher, A. Eckardt, S. Hilbert, J. Hutton, W. Kirchhofer, E. Lithopoulos, R. Reulke, S. Wicki. 2000. Design principles of the LH systems ADS40 airborne digital sensor. International Archives of Photogrammetry and Remote Sensing. 33:B1.