Update September 2010:
This is an ongoing and evolving project. The US Air Force is dropping 10 or
12 EM-APEX floats in front a typhoon near the Philippines this month. A new
version of E-Kermit has been deployed in the new floats, which implements
true (rather than simulated) sliding window transport protocol, plus some
other important improvements. These connections — from a buoy
floating in 20-foot seas in driving rain and gale-force winds communicating
with an earth satellites through non-error correcting modems to a home
station on the other side of the earth — pose one of the
toughest challenges that a file-transfer protocol can face
[read more...]
Hurricane Frances, 1 September 2004.
Photo: NOAA, Click image to enlarge
NEW YORK, 20 SEPTEMBER 2004
CHARLEY,
Frances, Ivan, Jeanne...
As the hurricane season of 2004 continues to inflict death and destruction
throughout the Caribbean, scientists are focussing on the role of ocean
currents, temperature, and salinity as they work to improve understanding of
hurricane behavior and develop better prediction models to save lives on
land and at sea.
Photo: Webb Research
To collect time-series ocean metrics, scientists and engineers at the
University of Washington Applied Physics Laboratory (APL) deployed
sensor-laden floats in the Atlantic Ocean in the path of the eye of
Hurricane Frances 31 August 2004. The floats, programmed to descend and
rise repeatedly to measure conditions as the hurricane approached and passed
by, were dropped from aircraft the day before the storm.
Webb Research
The devices, manufactured by Webb Research Corporation and called
Electromagnetic-Autonomous Profiling Explorers (EM-APEXs) with
instrumentation designed and built at APL, measure the ocean's velocity
electromagnetically while monitoring water temperature and salinity, with
excursions to depths of 500 meters every 16 hours. Each made more than 100
up-and-down profiles, mostly while under water, and then transferred the
data they had collected, along with GPS location, over the Iridium satellite
cell phone system to an onshore base station, using
The Kermit Project'sEmbedded Kermit
(E-Kermit) software, which had been integrated into the float's control
processor by APL Senior Electrical Engineer
John
Dunlap (pictured on the right, below, with float), a longtime Kermit
Project contributor, who describes Kermit's role in the project:
Photo:
U of Washington Applied Physics
Laboratory. Senior electrical engineers
Jim Carlson and John Dunlap with
the EM-APEX float.
Three of our floats were among the 40 scientific packages launched with
parachutes from an USAF
WC-130
Hercules
in front of Hurricane Frances north of Hispaniola. The data is all good and
all parties are pleased. The National Oceanic and Atmospheric (NOAA)
program is called
CBLAST
The EM-APEX float uses Embedded Kermit with an Iridium data modem,
a Motorola model 9522. C-Kermit is used ashore
on a Linux box with several serial ports and modems. The floats phone home,
log in, then give shell commands to start C-Kermit for data transfer.
Mission changes are implemented with a file sent to the float.
The integration and testing of E-Kermit 1.5 into the float's Philips XAG30
microprocessor took me several days.
We switched to Kermit because the Xmodem protocol was not recovering
reliably when bytes were lost. Ocean waves interrupt the signals when they
splash over the Iridium antenna which is only about a foot above the ocean
surface. We are very pleased to say that all data has arrived intact. This
is verified with an end-to-end CRC on each data group which is separate from
the Kermit type-3 CRC used used in the actual transfer. The EK addition is
fantastic for this application.
John leaves Thursday (September 23rd) on a cruise to collect the floats.
Embedded Kermit is ideally suited for applications like this.
E-Kermit is the product of more than 20 years' experience with design and
real-world implementation of file-transfer protocols that are resilient under
harsh conditions, yet can go fast when sailing is smooth. E-Kermit is
especially designed for embedding in microcontrollers, where reliable
unattended operation in the smallest possible memory footprint is a must.
In this application, E-Kermit occupied just 9710 bytes; customer-supplied i/o
routines another 4266 bytes, and the customer-supplied control loop 15102
bytes, a total of 29KB.
