Full text: Remote sensing for resources development and environmental management (Volume 2)

Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986 
Rainlog and preslog: Novel tools for in-situ measurements 
D.de Hoop 
International Institute for Aerospace Survey and Earth Sciences (ITC), Enschede, Netherlands 
The rainlog and preslog electronic water level log 
gers were developed at the International Institute 
for Aerospace Survey and Earth Sciences (ITC), 
Enschede, and after some redesigning, are produced 
by Siemens Netherlands, The Hague. 
The instruments measure and record water pressure 
over long periods (for example, at sixty minutes 
intervals for a period of 12 months) without requir 
ing maintenance or changing of batteries. Expensive 
test stations are not required. The loggers, togeth 
er with the data-processing facilities, provide a 
new scientific approach to field measurements. 
The pressure recordings ar.e controlled by a micro 
processor and are stored in a removable internal 
memory block (the "Eprom"). The capacity of the 
Eprom is 10240 records. The records are read by a 
personal computer (Epson, type PX-8) with an "Eprom 
reader". Depending on the software chosen the re 
sults can be presented raw or in calculated form. 
Two types of loggers are available; both have the 
same electronics. The difference is based on the 
type of sensor used. Rainlog has a relative pressure 
sensor; preslog has an absolute pressure sensor. The 
standard range for rainlog is 2 meters. The standard 
range for preslog is 0 to 4 bar, which at sea level 
is equivelent to a range of 30 meters. 
The precision of the measurements is approximately 
0.2 percent for preslog and 0.5 percent for rainlog. 
The resolution is 2000 for the rainlog and 4000 for 
the 4 bar-type preslog. The measuring interval can 
be set between 30 seconds and 60 minutes (60 minutes 
is standard). A built-in audio signal provides an 
operational check. 
The loggers were designed for both accuracy and 
durability. Durability requires permanent attachment 
to the internal panel of all parts except the remov 
able memory block (Eprom) and also very firm place 
ment of the panel in the steel cylinder. Opening the 
cylinder to replace the Eprom or to re-set the re 
cording interval requires a vise, which is usually 
not available at a test site. We therefore recommend 
transporting the entire logger to a field office 
where the necessary equipment can be kept and where 
there is less danger of damage to the Eprom. 
1.1 Preslog applications 
River level 
To record river levels, a logger must be anchored 
in the riverbed. After installation, it is left for 
a maximum period of 12 months. The instrument func 
tions without disturbance, despite shifting bottom 
sand and gravel. After the operating period, the 
logger must be retrieved and opened; the memory 
block is removed and read by the personel computer. 
An additional "dry" preslog is required for barome 
tric correction. One dry logger covers an extensive 
area and thus can be combined with several wet 
Groundwater level 
Preslog can also function as a groundwater level 
logger. Its three inch diameter allows placement in 
waterpipes for pump-test. Data from several tests 
can be recorded in sequence by placing a "marker" 
in the recorded data to indicate the end of one 
test and the beginning of the next. 
1.2 Rainlog applications 
To record rainfall, a rainlog is connected to the 
bottom of a rain collection container. Only in 
creases in pressure are recorded. Decreases in 
pressure caused by evaporation or emptying the 
container are ignored. A simple program later shows 
the results of a year's data collection.

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