EM 1110-2-2907
1 October 2003
(2) A histogram plot of the digital number value assigned to each pixel in the scene
clearly reveals three distinct spectral populations. These three classes were determined to be
wild rice growing in the lake, wild rice in marsh, and wild rice in a saturated soil. Wild rice
growing in shallow or marsh water produced pixels that overlapped with more than one
class. The near-infrared (N-IR) band allowed for better spectral separation by eliminating
the effect of varying amounts of water in the substrate.
f. Conclusions.
(1) An estimate of the acreage percent based on a supervised classification determined
that 1% of the scene was dominated by wild rice. Habitat was shown to predominately exist
along the lakeshore, at inlets, ponds, on banks, and in marsh areas. Wild rice was deter-
mined to grow in saturated soil, marsh, and in shallow lake waters. The author recommend
200 ground truth points be collected per class (100 for spectral determinations and 100 for
classification designation). Application of the ground truth data to a SPOT scene collected 5
days after the ground truth data did not produce an accurate classification. This test reveals
the limitations on the usefulness of SPOT data for surveying vegetation--ground truth must
be collected at the time of data acquisition.
(2) A detailed map of the distribution of wild rice will allow land managers to better
predict the impact of changes in water level and phosphorous input on the natural produc-
tion of wild rice.
Point of Contact: Robert Bolus, Phone: (603) 646-4307
6-9 Case Study 7: Duration and Frequency of Ponded Water on Arid
Southwestern Playas
Subject Area: Hydrology.
Purpose: To delineate playa inundation frequency and duration.
Data Set: Multispectral/thermal (Landsat 4, 5, and 7 and MTI Multi-spectral Thermal
Imager).
a. Introduction.
(1) Playas are ephemeral shallow lakes found in the arid southwest United States.
Their hydrology is dominated by rainfall and runoff in the wet season and evaporation
throughout most of the year. Surface hydrology, particularly frequency and duration, is
poorly understood in the playa environment. US waters, including playa water, are Federally
regulated under article 33 CFR 328.3 [a] of the Clean Water Act. Water bodies are deline-
ated to their outermost extent termed their "Ordinary High Water" (OHW). OHW is defined
by the presence of physical hydrological features representing the ordinary reaches of high
water in its bed or basin.
(2) Playas exhibit tremendous temporal variation, as they may not pond at all during a
particular year or may remain ponded for several years. The extent to which water remains
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