2021 Washington NAIP 4-Band 8 Bit Imagery

Downloadable Data

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DOQQ Production Process Description;

USDA FSA APFO NAIP Program 2021;

The imagery was collected using the following digital sensors:

Vexcel Condor M4.1 (Serial Number 435S52516X011066),

Vexcel Condor M4.1 (Serial Number 435S72614X210073),

Cameras are calibrated radiometrically and geometrically

by the manufacturer.

Collection was performed using a combination of the

following twin-engine aircraft with turbines flying

at 17,000 ft above mean terrain.

Plane types:

C441 Cessna Conquest

Tail numbers:

N440EH,

N441MD,

With this flying height, there is a 30% sidelap,

giving the collected data nominal ground sampling distance

of 15cm and rectified to 60cm.

Based-upon the CCD Array configuration present in

the Condor sensor, imagery for each flight

line is 48,460-pixels in width. Red, Green, Blue,

Near-Infrared and Panchromatic image bands were collected.

The Vexcel Condor has the following band specifications at 40% intensity:

Red 585-690,

Green 570-600,

Blue 425-530,

Near Infrared 700-830,

all values are in nanometers.

Flight planning was performed in IGI Plan over a

buffered boundary covering DOQQ extents provided by the USDA.

A 500m reduced resolution DEM file was used to determine

ground heights. A targeted flight altitude of approximately

17,000 feet above ground level for native 15 cm image

acquisition with sidelap of 30% was used

for flight planning parameters. Multiple aircraft were utilized

for acquisition, the seamline

shapefile clarifies which aircraft were used for a given area.

All aircraft were equipped with Vexcel

Condor systems where utilized for data

capture. The Vexcel Condor sensor

has been calibrated by the manufacturer as well as validated

against a local calibration range. The calibration includes

measuring the radiometric and geometric properties of the

camera. This data is used in the Post Processing Software

to eliminate the radiometric and geometric distortion.

All aerial imagery was collected with associated GPS/IMU

data. Condor collection requires high quality IMU data for

processing and was critical for early access hosting of digital

data to the web for USDA interim access and review.

After early access web delivery was complete, all

imagery was triangulated using Vexcel Ultramap in which

the airborne GPS data was constrained to expected limits.

To validate the accuracy of the block adjustment derived from

GPS/IMU, sensor parameters and conjugate point measurements,

photo identifiable ground control points were field surveyed within

each State. These points were surveyed using GPS techniques to

produce coordinates that are accurate to +/- 0.25 meters RMSE in XYZ.

The GPS surveying techniques utilized assured that the coordinates

are derived in the required project datum and relative to an approved

National Reference System. Once the block has proper statistics and fits the

control to specifications, the final bundle adjustment was

made.

The final adjustments assure a high quality relative adjustment

and a high quality absolute adjustment limited to the

airborne GPS data accuracy. This process assures the final

absolute accuracy of all geopositioned imagery. Both

signalized and photo identified ground control were used to

QC and control the IMU/GPS based aerial triangulation bundle

block solution. Surdex Grouping Tool provides real-time updates

of the USDA APFO Image Metrics. The image technician adjusts

image correction parameters to bring the radiometric

characteristics of large groups of images within the Image

Metrics ranges. For each project area the highest resolution

DEM or LiDAR was obtained and utilized for rectification of captured

imagery.

A visual inspection of the final DEM using color cycled

classification by elevation and a shaded relief was performed

to check for gaps, corruption and gross errors.

The predicted horizontal error for each

point was added as an attribute in the SURDEX enterprise

database. An operator reviews ortho seams

in areas these predicted errors indicate horizontal error in

excess of the contract specifications. Any imagery errors

introduced by source DEM required patching from an alternate

perspective or strip of photography.

Processing hardware used included various brands of survey grade

GPS receivers, various brands and models of computers,

RAID6 storage, calibrated monitors, various brands of monitor

calibration colorimeters. Vexcel Ultramap was used for post

processing of Condor data, and triangulation.

SURDEX software was used to orthorectify, color correct,

and remove bidirectional reflectance, vignetting and other

illumination trends. USDA APFO Image Metrics are measured and

images corrected to conform to the Image Metrics using

SURDEX software. GPS/IMU data was reduced to projected

coordinates in the appropriate UTM zone using

Applanix POSPac. SURDEX software was used

to calculate the optimal seam path, check seam topology and

create master tiles. SURDEX ortho software generates

occlusion/smear polygons used during seam review

of steep terrain. SURDEX software was used to

visually inspect master tiles for seam and image defects.

SURDEX software was used to project and cut final DOQQ image

files from masters. SURDEX software was used to create CCM

metadata. Lizardtech GeoExpress version 10.0.1.5035 was used

to create the CCM image file. SURDEX software was

used to perform final formatting, QC and naming of the DOQQ.

USGS metadata parser software was used to validate the metadata.

Various versions of Microsoft Windows were used in all phases of

production. Grouping Tool was used again after DOQQ and CCM

production to provide a quality assurance check. Individual

DOQQ and CCM may not meet the USDA APFO Image Metrics ranges

due to land cover. The goal is to have the state as a

whole meet the Image Metrics. All products are reviewed

by independent personnel prior to delivery.

The delivery is checked for omissions, commissions,

naming, formatting, specification compliance and data integrity.