U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2007–3087

September 2007

Prepared in cooperation with the U.S. Army Corps of Engineers, Missouri River Recovery Integrated Science Program

Assessment of Least Tern and Piping Plover Habitats on the 

Missouri River Using Remote Sensing

Printed on recycled paper

Emergent sandbars in the Missouri River are critical 

breeding habitat for the endangered interior population of 

least terns (Sterna antillarum) and the threatened Northern Great Plains population of piping plover (Charadrius 

melodus). A fundamental challenge in riverine habitat 

evaluation is dealing with the spatial and temporal 

variability resulting from variation in river discharge. 

Small changes in discharge can result in large changes 

in the area of available habitat on low-relief emergent 

sandbars.

Remotely sensed imagery with high spatial resolution 

can be used to inventory and map the amount, composition, and juxtaposition of land-cover categories on 

emergent sandbars at a single instant in time. Interpretation of habitat estimates and trends would be simplified by 

acquisition of remotely sensed imagery at a similar river 

discharge at each observation period. However, 

it is extremely challenging to achieve this 

image acquisition goal in practice. 

Alternatively, flow-related variability 

in habitat estimates can be modeled 

using imagery acquired at multiple 

times at a range of discharges, and 

correlating habitat areas with 

discharge. Quantification 

of emergent sandbar 

area and habitats 

on multiple dates 

provides a better 

characterization of 

least tern and piping 

plover habitat relative 

to estimates from a single 

date.

Hydraulic models are an 

alternative method to estimate the 

area of emergent sandbars as a 

function of discharge. Bathymetric and topographic survey data 

are a primary data component of hydraulic models and 

are difficult and costly to obtain compared to optical 

remotely sensed imagery. Furthermore, small errors in 

model predictions of water surface elevation can lead to 

large errors in estimates of the area of low-relief emergent 

sandbars, so the utility of these models needs to be evaluated in context of costs, uncertainties, and information 

content.

Synergistic use of optical remotely sensed imagery 

and elevation models is a promising approach to riverine 

habitat evaluation. Optical remotely sensed imagery can 

be used to inventory habitat characteristics, for example, 

plant communities and successional stages, which are 

not obtainable from hydraulic models, and can be used to 

evaluate predictions of sandbar inundation.

Research Goal and Strategy

The primary goal of this study is to develop a costeffective method to inventory, map, estimate, monitor, 

and evaluate least tern and piping plover habitats for 

four segments of the Missouri River using 

remotely sensed imagery (fig. 1). 

The inventory and mapping 

objective is to develop a 

database of the spectral and 

spatial properties of habitat 

categories from analysis of a 

collection of multitemporal 

remotely sensed images and 

methods to identify and map 

habitats. The estimation objective uses probability-based accuracy 

assessment of the habitat maps to calculate unbiased estimates of the area of habitat 

categories with standard errors by accounting 

for omission and commission errors in the maps. 

The monitoring objective uses analysis of the 

habitat maps from different dates to quantify 

accretion and erosion of sandbars, vegetation 

succession, bank erosion, and other temporal 

dynamics in the riverine system. The evaluation objective uses generalized linear models 

to relate nest density and nest success to 

habitat metrics derived from the remotely sensed imagery. 

Replication provided by multisegment (Gavins Point, Fort 

Randall, Garrison, and Fort Peck segments of the Missouri 

River) and multiyear analyses will allow assessment of 

Upper right photograph: Least tern (Sterna 

antillarum) by S. Maslowski. Lower left 

photograph: Piping plover (Charadrius 

melodus) by Gene Nieminen. Photographs 

courtesy of U.S. Fish and Wildlife Service.
the confidence and generality of the predictive value of 

the habitat variables for describing habitat selection by the 

birds.

A two-pronged approach provides a cost-effective, 

relatively simple method to meet the U.S. Army Corps 

of Engineers short-term habitat mapping and monitoring 

needs for all four river segments while simultaneously 

evaluating more complex techniques on the Gavins Point 

segment for possible future monitoring efforts. Pansharpened multispectral QuickBird imagery (http://www.

digitalglobe.com) is being acquired for all four river 

segments in 2006–08 (fig. 2). Two image acquisitions are 

attempted for each year: one during the nesting period 

and the other during the brood rearing period. Imagery is 

analyzed using hierarchal object-based image 

segmentation and classification procedures in Definens 

Developer software (http://www.definiens.com).

For the Gavins Point segment, QuickBird 

imagery was also acquired in 2005 during June-July 

(594.7 m3/s discharge from Gavins Point Dam), September (707.9 m3

/s), and October (254.6 m3/s), and LIDAR 

data were collected in November 2005 (311.5 m3/s). 

Approaches for predicting sandbar inundation vary in 

data requirements and assumptions. The Missouri River 

downstream from Gavins Point Dam is regulated to 

produce steady to gradually varying flow for long time 

intervals during typical years. Under these conditions, 

water-surface elevations can be approximated as sloping 

planes along the river, and water-surface elevations for 

discharges of interest can be interpolated between river 

gaging stations. By subtracting the planar water surface 

from the bare earth elevation model derived from the 

LIDAR data, sandbar inundation predictions can be made 

for areas which were above the water-surface at the time 

of the LIDAR acquisition (fig. 3). Model predictions 

of sandbar inundation at discharges corresponding to 

the time of QuickBird acquisitions can be evaluated by 

comparison with habitat maps produced from analysis of 

the QuickBird images (figs. 4 and 5). This approach is 

simple, avoids the need for extensive bathymetry data, and 

avoids the expense of compiling, calibrating, and validating hydraulic models. A hydraulic model and bathymetry 

data would be appropriate if the objective was to simulate 

a flood wave, to model inundation at discharges for which 

Figure 1. Missouri River and location of four river segments identified in the U.S. Fish and Wildlife Service 2003 amendment to the 2000 

Biological Opinion on operation of the Missouri River (http://www.nwd-mr.usace.army.mil/mmanual/FinalBO2003.pdf).
Figure 2. QuickBird color infrared composite for a 2.5-km reach on the Gavins Point segment. Image was acquired May 12, 2006, when 

discharge from Gavins Point Dam was 455.9 m3 /s.

30 cm Inundated

15 cm rInundated r0 cm

0 cm Exposed 15 cm

30 cm rInundated 15 cm

30 cm bExposed 45 cm

45 cm bExposed 60 cm

15 cm bExposed 30 cm Exposed r60 cm

EXPLANATION

Figure 3. Predicted sandbar inundation corresponding with May 12, 2006, QuickBird acquisition. Colors represent depths of water or heights 

of exposed surfaces in relation to water surface elevations.
stage measurements were not available, or to calculate 

a flow velocity. It may also be necessary to use hydraulic models if water-surface irregularities would produce 

significant longitudinal errors in predictions of inundated 

areas.

A preliminary evaluation of the sandbar inundation 

modeling for the Gavins Point segment corresponding to 

June 2005 and July 2006 QuickBird imagery has been 

completed. The agreement between measured (QuickBird 

imagery) and predicted sandbar inundation was good. 

Low-elevation portions of sandbars with a wet substrate 

account for the majority of the commission errors in the 

inundation predictions (analysis of QuickBird imagery 

reveals locations are above the water surface but the 

model predicts inundation). Omission errors for inundation predictions (analysis of QuickBird imagery reveals 

water at the locations but the model predicts the sandbars 

are not inundated) are the result of an estimated water 

surface slightly less than the bare earth elevation. Temporal changes in the distribution of sand between dates of 

QuickBird imagery and LIDAR undoubtedly account for 

some of the prediction error, as does non-planar water 

surface elevations. The strength of the agreement between 

model predictions with habitat maps from 2007 and 2008 

QuickBird imagery will provide a measure of the useful 

lifetime of the bare earth elevation model derived from 

the November 2005 LIDAR data in this dynamic river 

environment.

Any use of trade, product, or firm names is for descriptive purposes only and 

does not imply endorsement by the U.S. Government.

For information contact:

Larry Strong, Wildlife Biologist

U.S. Geological Survey

Northern Prairie Wildlife Research Center

8711 37th Street SE

Jamestown, ND 58401

701-253-5524

lstrong@usgs.gov

Figure 4. Upper level of two-level hierarchal habitat classification 

scheme for May 12, 2006.

Figure 5. Lower level of two-level hierarchal habitat classification 

scheme for May 12, 2006.

Island

Flood plain

Water

Sandbars attached (sandbars not surrounded by water

 at time of imaging) and flood-plain shoreline

EXPLANATION

Water

Wet substrate

Herb and shrub vegetation, sparse

Dry sand

Woodland

Flood plain

Herb and shrub vegetation, continuous

EXPLANATION