Project L: Remote Sensing 

Overflight in Support of LongTerm Monitoring and LTEMP

Annual Reporting Meeting – January 12, 2022

Joel B. Sankey, USGS, Southwest Biological Science Center, Grand 

C anyon M onitoring and R esearch C enter

T homas G ushue, U SG S, SB SC , G C M R C

K eith K ohl, U SG S, SB SC , G C M R C

L aura D urning, N AU
Goals, Objectives, Results

Imagery and derivative data products from 

overflight remote sensing are used either directly 

or indirectly by every science project proposed in 

this TWP to address every resource goal of the 

LTEMP

Science Questions: 

• How has landcover changed in the 

Colorado River Ecosystem (CRe) in 2021 relative 

to preceding decades? 

• How are observed landcover changes 

related to dam operations, other land use and 

management activities, as well as climate and 

other environmental factors in the ecosystem? 

Little Colorado River 

Confluence – May 2021

Preliminary data – do not cite
May 2021 

Overflight 

Deliverables

Imagery:

4 band 

Orthomosaic

Imagery:

All raw flightlines

Topography:

Digital Surface 

Model & Digital 

Elevation Model

Preliminary data – do not cite
May 2021 Overflight status

QA/QC Evaluation Steps

o Examine orthomosaic pixel values from key 

feature types (examples: dry sand, shadow, 

vegetation, etc.)

o Compare tile overlaps in orthomosaic and

topographic elevation models

o Compare X and Y coordinates to known 

placed ground truth panels

o Compare Z values to low flow concurrent 

ground truth survey data
May 2021 Overflight Imagery Positional (Horizontal) Accuracy

 156 black and white ground truth panels 

were placed between Glen Canyon Dam 

and Pearce Ferry to assess positional 

accuracy on the Earth surface.

 Many of the same ground truth locations 

were also occupied in previous overflights 

allowing GCMRC to accurately assess 

positional accuracy between overflights.

Total Northing (y) Easting (x)

RMSE 0.521 0.436 0.284

95% Confidence 1.274 0.855 0.557

2021 accuracy to Survey Control (meters)

Results subject to change following Fugro’s revision of deliverables in 

response to USGS QA/QC (Preliminary data – do not cite)
May 2021 Overflight Topography Positional (Vertical) Accuracy

 23 sandbars were topographically surveyed during the 

overflight steady low flows. 

 We used the interpolated survey surfaces for these bars 

to evaluate the accuracy of the DEM & DSM datasets.

RMSE 0.296

95% Confidence 0.580

DEM Accuracy

137.7mile bar – 2021 Mosaic

Results subject to change following Fugro’s revision of deliverables in 137.7mile bar – 2021 DEM

response to USGS QA/QC (Preliminary data – do not cite)
Measurement of water-surface profile during 2021 

overflight

• Continuous profile collected by 

boat from Lees Ferry to Pearce 

Ferry

• 187 surveyed water surface 

elevations at (1 every ~1.2 miles)

• 23 topographic surveys for 

validating the overflight digital 

elevation model

• All water-surface and topographic surveys have 

been processed

• Preliminary comparison between 10 surveyed 

water-surface elevations and boat-based 

measurements indicate improved accuracy 

(maximum difference of 0.11 m with mean 

difference of 0.02 m)
Measurement of water-surface profile during 2021 

overflight

• The water-surface profile at a constant discharge 

(8,000 cfs) is used to delineate the river shoreline 

and is used to calibrate models for predicting the 

water surface at other discharges

• The best profile currently available is based on lidar 

data collected in 2000

– Accuracy of water-surface elevations estimated to be ± 0.5 

m, based on limited ground-truth data

– 0.5 m vertical error can equal 25 m or more horizontal 

error in shoreline location

• Purpose of 2021 effort:

– Measure continuous profile from at least two sources

• Overflight digital surface model (lowest ground surface elevation 

adjacent to water)

• Moving boat with high-accuracy GNSS receivers

– Verify accuracy with surveyed check-points throughout 

river corridor

From Magirl et al. (2008)
Continued Analysis of 2013 and Earlier 

Overflight Imagery

• 2 papers published in 2021

• Durning et al., 2021

• Bransky et al., 2021
Hydrologic and geomorphic effects on riparian plant 

species occurrence and encroachment: remote sensing of 

360 km of the Colorado River in Grand Canyon
Durning et al, 2021
Summary (Durning et al. 2021)

• Riparian vegetation expanded from 2002 to 2013.

• Three quarters of the expansion occurred between 2002 &

2009.

• Seep willow, tamarisk and arrowweed were the primary

encroaching woody species.

• Common reed and horsetail were the primary encroaching

herbaceous species.

• Encroachment composition from 2002 to 2009 was similar to the

entire riparian landscape, whereas encroachment from 2009 to

2013 primarily consisted of seep willow and early colonizing

herbaceous species.

• Emergence of seep willow and arrowweed after burial by sand

deposited by controlled floods indicated that those species were

resilient to this form of disturbance.

• Describing patterns of species encroachment is an important

step towards designing flow regimes that favor riparian species

and ecosystem functions valued by stakeholders
Monitoring Tamarix Changes Using 

WorldView-2 Satellite Imagery in Grand 

Canyon National Park, Arizona
Summary (Bransky et al. 2021)

• We used highly accurate classifications derived from

overflights and satellites to map changes in tamarisk cover

• During the growing season of 2019 we documented a

47.5% decline in tamarisk

• At the decadal scale, we observed a 29.5% decline in

healthy tamarisk canopy between 2009 and 2019

• (note 2021 overflight imagery will provide system-wide

update on beetle impacts to tamarisk)

• These maps provide detailed information that can allow

managers to target mechanical and other invasive species

management efforts
Thank you for listening!

Durning et al. (2021). Hydrologic and 

geomorphic effects on riparian plant 

species occurrence and 

encroachment: Remote sensing of 

360 km of the Colorado River in 

Grand Canyon. Ecohydrology, 

e2344. 

https://doi.org/10.1002/eco.2344 

Branskyet al. (2021). Monitoring 

Tamarix Changes Using 

WorldView-2 Satellite Imagery in 

Grand Canyon National Park, 

Arizona, Remote Sensing, 

https://doi.org/10.3390/rs13050958

Airborne remote sensing 

webpage

USGS Grand Canyon 

Monitoring and Research 

Center