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Senior Design 04-05: Team 10

The Sky's the Limit

A Global System for Monitoring Earth Radiation Balance

Llian Breen, Aaron Buys, and John Vander Weide
Dr. Matthew K. Heun

Prof. Huen and Calvin logo


Group members: Aaron Buys, John VanderWeide, and Llian Breen

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Accurate global outgoing radiation measurements are important for the modeling of atmospheric, weather, and global warming phenomena. The present method for collecting radiation data for the Earth’s radiation balance involves satellites and scientific balloons. Through the use of scientific balloons flying at 35 km and active cavity radiometers (ACR), the uncertainties inherent in the satellite data can be eliminated. Last year’s project objectives involved the thermal and electrical design of an Active Cavity Radiometer for an atmospheric balloon. For the 2004-05 project year, Finalizing this design, constructing prototypes, and a demonstration of concept balloon flight are proposed.


The Earth’s radiation balance includes the solar radiation incident on the earth’s atmosphere, and the re-radiation/reflection of short and long wave radiation from the Earth. Figure 1 shows the outgoing long wave (5-100 µm) thermal IR radiation from the Earth. Figure 2 shows the reflected short wave (0.3-5 µm) solar visible radiation leaving Earth.

Earth radiation map for outgoing long wave and reflected short wave

Active cavity radiometers are used to collect global and solar radiation data from satellites through NASA programs such as ACRIM and ERBS. Radiation data such as Figures 1 and 2, is used in predictive models of Earth’s surface temperature and cloud/precipitation weather.

Advantages of 35 km Data Collection

Balloon flight graphic from Global Aerospace

Many weather models assume the top of the atmosphere at 35 km. Current radiation measurements are obtained by satellite based instruments more than 800 km above the earth’s surface. Satellite data is extrapolated to 35 km for use in weather models. Direct collection of hemispherical data at 35 km by scientific balloons has the following advantages:

Reduces modeling of vegetation and albedo
Reduces sources of modeling uncertainty
Allows longer measurement time over target
Provides a full hemisphere of data collection

Satellite vs. Ballon radiation detection

The active cavity radiometer plays a central instrumentation role in both satellite and proposed balloon radiation measurements of the earth’s radiation balance. With the weather balloon system shown in Figure 5, the ACR measures directly the outgoing radiation 35 km.

Design Objectives

Project objectives include the redesign of an active cavity radiometer for flight on a weather balloon, fabrication of several ACR prototypes, lab based testing, and a demonstration of concept balloon flight in Spring 2005. Analysis of gathered balloon flight data provides an experimental calibration of the ACR prototype and validation of both thermal modeling and overall design.

Balloon and ACR diagram

The 2003-04 project group designed a demonstration prototype for a 35 km scientific balloon. During the upcoming project year, a working prototype will be built through redesign of the ACR for a radiosonde weather balloon system. Specific changes include:

Revamping the feedback system
Altering transmission system for the radiosonde
Enhancing the A/D conversion
Rescaling of prototype geometry

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