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3,2 Site Description
The Pakri Peninsula, shown in Figure 1, is located
approximately 42 km west of the city of Tallin and includes
the smaller towns of Paldiski and Leetse. The peninsula
extends into the Gulf of Finland, has moderate to heavy
vegetation, and the elevation averages 11 - 23 m above
mean sea level. The Paldiski Naval Reactor Training Facility
was comprised of two reactors used for training Soviet
submarine crews. Reactor operations ceased in 1994, with
transfer of the facility from Russia to Estonia occurring on
October 1, 1995.
3.3 Operations
An area of approximately 90 km? in size was surveyed during
a two-week acquisition period (June 15-26, 1995). All
necesary equipment, including a MBB BO-105 helicopter
used for the aerial acquisitions, was shipped to Estonia for
the survey.
Radiological results were processed onsite and
superimposed on maps and satellite imagery of the site. The
objectives of the radiation analysis were to: 1) ascertain data
integrity, 2) establish the spatial distribution of the gamma
radioactivity, 3) identify the radionuclides contributing to the
gamma exposure, and 4) estimate the quantity of
radionuclides present relative to the exposure rate and annual
dose.
Multispectral scanner (MSS) data processing began
immediately following the first MSS flight. Processing
involved decommutation which is the conversion of an
analog, serial, bit data stream to a digital format that is
readable by computers. MSS data was recorded on a high
density data taped and then decommutated into a computer
compatible file format. The MSS data was then quality
checked in the field and assessments were made to
determine if MSS objectives were met. Analysis was
performed upon return to RSL. This paper summarizes the
preliminary results of the survey.
4. DATA DESCRIPTION
To meet the project goals, multiple sensor systems were
flown on the BO-105. Table 1 lists the parameters
associated with each type of data collected including ground
based radiation measurements.
4.1 Aerial and Ground-Based
Radiological Surveys
The radiological Survey capabilites are a unique and valuable
resource for sites where radioactive materials may be
Present. The data collection system that makes up the
arbore element is comprised of highly specialized
équipment developed by RSL This equipment
simultaneously collects location and gamma spectral radiation
data. These data are routinely calibrated to represent surface
intensity levels as well as exposure rates for specific
radionuclides,
309
The airborne portion of the nuclear radiation measurement
system detects and records gamma radiation levels with
positions determined by a differentially-corrected Global
Positioning System (GPS).
There are two nuclear radiation sensor pods that are
mounted below the BO-105 helicopter. In these pods, there
are eight downward-looking 2 x 4 x 16-in and two 2 x 4 x 4--in
upward-looking thallium-activated sodium iodide, Nal(T/),
scintillation crystals for gamma radiation detection.
Ground-based radiation measurements were collected using
a high purity germanium (HPGe) detector system for gamma
ray spectroscopy. A pressurized ion chamber was used to
measure exposure rates.
Together, the ground-based and aerial radiation collection
systems provided three pieces of information: 1) established
the spatial distribution of the gamma radioactivity, 2) identified
the radionuclides contributing to the gamma exposure, and
3) estimated the quantity of radionucleides present relative to
the exposure rate. To achieve the desired results,
isoradiation count rate contours of natural and man-made
Sources were generated and superimposed on aerial
photography taken during the timeframe of the radiation
survey.
4.2 Airborne MSS Survey
The multispectral element of the multisensor survey used a
Daedalus AADS1268 MSS electro-optical scanner to collect
data. It is one of three Daedalus scanners maintained and
operated by the RSL for DOE applications. MSS systems
are flown on a regular basis and the collected data are used
for a variety of environmental and target signature
applications.
The airborne Daedalus multispectral scanner resolution is
altitude dependent. It has an instantaneous field of view of
2.5 milliradians and a total field of view of 85.92 degrees in
eleven spectral bands. In the Paldiski survey, flight altitudes
of 1000 m have a ground sample distance (GSD) of 2.5 m,
152 m altitude has a GSD of 38 cm, and 91 m altitude has a
GSD of 22 cm. Spectral bands are available in the visible,
near infrared, middle or short-wave infrared (SWIR) and the
thermal infrared regions of the electromagnetic spectrum.
Aerial photography was obtained concurrently with
multispectral imagery. While the photography has
comparatively limited spectral utility, it does provide very fine
spatial detail and overlapping coverage for stereo viewing. In
general, successful support of environmental remediation
programs results from using both sensors together; that is,
many applications require both good spatial and spectral
information.
For some applications, the unique features of the airborne
MSS systems operated by RSL offer major advantage over
traditional aerial photography and commercial remote sensing
satellites. The scanners collect spectral response at
wavelengths that are impossible to collect with aerial
photography. By flying at lower altitudes, the scanners can
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
