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D5518-94 – Standard Test Method Technical Guide
🗂️ Scope and Sourcing for Historic Site-Use Analysis
This guide is intended to assist potential users in the search for, evaluation of, and acquisition of remotely sensed aerial photography or imagery for the purpose of establishing the historic site-use and other interpretable surface or near-surface conditions regionally, locally, or at a specified project location. The instructions given within identify sources of photography and imagery, and provide information pertaining to the specifications, characteristics, and availability of these data.
💡 Key Consideration: The major sources considered in this guide are restricted to federal and state organizations only. The sources described do not represent all possible sources of interest for environmental and engineering applications.
📸 Key Film and Imagery Specifications
The standard defines several critical film types based on their spectral sensitivity and application. Understanding the specific wavelength ranges and corresponding limitations is essential for selecting the appropriate imagery for a project.
| 🟦 Film Type | 📏 Spectral Range (µm) | 🎯 Primary Applications | ⚠️ Technical Limitations |
|---|---|---|---|
| Black-and-White Infrared (IR) | 0.5 to 0.9 (Exposed) | Detection of vegetation types, diseased plants, soil/rock conditions, land/water boundaries. | Requires absence of blue exposure for haze penetration; interpreted within constraints of data collection. |
| Conventional Color (Natural Color) | 0.4 to 0.7 (Visible) | Identifying soil types, rock outcrops, industrial stockpiles, shorelines. | Limited by “fogging” (poor haze penetration) associated with exposure to blue wavelengths. |
| Color Infrared (Color IR) | False-color reversal film, exposed as B&W IR. | Enhanced visual differentiation of natural features using false-color rendering. | Absence of exposure to blue wavelengths allows for similar haze penetration as B&W IR film. |
⚙️ Practical Application and Professional Judgment
Users must recognize that this guide offers an organized collection of information and a series of options, rather than a specific course of action. The standard emphasizes that it cannot replace education or experience and should be used in conjunction with professional judgment. Furthermore, the document is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should it be applied without consideration of a project’s many unique aspects. The values stated in both inch-pound and SI units are to be regarded separately as the standard.
🚨 Important Disclaimer: As per Section 1.6 of the standard, this ASTM guide is not a substitute for professional expertise. Not all aspects of this guide may be applicable in all circumstances. The word “Standard” in the title means only that the document has been approved through the ASTM consensus process.
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D5518-94?
The guide is intended to assist users in the search for, evaluation of, and acquisition of remotely sensed aerial photography or imagery for establishing historic site-use and other interpretable surface or near-surface conditions.
💡 What are the three main film types detailed in the terminology section?
The terminology section of the standard defines Black-and-White Infrared (IR) film, Conventional Color (Natural Color) film, and Color Infrared (Color IR) film, each with distinct spectral sensitivities and applications.
⚡ Why is Black-and-White IR film superior for haze penetration?
B&W IR film is exposed using only green through reflective IR wavelengths (0.5 to 0.9 µm). By avoiding exposure to blue wavelengths (0.4 to 0.5 µm), which are highly scattered by atmospheric particles, it overcomes the “fogging” effect that degrades conventional color film.
📌 How should the units given in the standard be interpreted?
The values stated in both inch-pound and SI units are to be regarded separately as the standard. The values given in parentheses are for information only.