HIAPER Airborne Radiation Package

Short Name or Variable Name:

HARP

HAIS Instrument:

Yes

Files & Brochures

HARPSpares.pdf

Instrument Type:

Radiometer

Manufacturer or Builder:

TABS

Description

Model:

none

Measurements Provided:

Actinic Flux and Stabilized Spectral Irradiance

General Description:

The instrument consists of two components:
- actinic flux: 280-680 nm, spectrally resolved, up and down
- This system consists of two hemispheric light collectors, each connected by fiber optics to a monolithic solid state spectrograph with a CCD detector. The spectral resolution is about 1.8 nm, and the field of view is the full sky up and down. The measurements then characterize the radiation environment responsible for photochemistry. The upward-viewing light collector is mounted on the top of the tail to avoid shielding by the tail.
- spectral irradiance: 260-2217 nm, spectrally resolved, on stabilized platforms up and down
- This system consists of spectrometers viewing up and down. A light collector with response proportional to the cosine of the incident radiation delivers the radiation to the spectrometers. To extend the range of wavelengths, two spectrometers are used in each direction; one is used to extend the wavelength coverage into the near IR.

The spectral characteristics of both components are summarized in the following table:
- ,
The HARP rack:
The HARP collectors. Clockwise from upper left: actinic flux, nadir; actinic flux, zenith; irradiance, nadir; irradiance zenith.
- ,

Measurement Characteristics:

Overall estimate of uncertainty: 4-6% for spectral actinic flux; 3-5% for spectral irradiance
Response time: samples collected at 1-10 Hz for actinic flux and 1-2 Hz for irradiance. Instrument response is faster than this.
Precision: 1%, both actinic flux and irradiance

Calibration Methods:

The instrument requires periodic calibration for absolute power via NIST traceable standard lamps. Calibrations can also check wavelength accuracy using line sources, and angular dependence of the sensors is also tested during calibration, but the absolute power calibration is the procedure needing frequent use. Laboratory calibration is needed prior to and after each deployment, and field calibrations are also needed to monitor changes in the instrument.

History of Significant Changes:

2009: Stabilized platforms reconfigured to accept direct GPS antenna feed instead of GPS receiver feed, whose delay exceeded the maximum allowed for proper stabilization.
2011: Stabilized platform software upgraded by Enviscope GmbH to allow manual input of platform limits. Prior version did not allow operation in the case of automatic limit detection failure.
2012: Following a failure during TORERO, the stabilized platforms were repaired and modified by Enviscope. Drive motor clutches were installed and the limit switch circuitry was refurbished to prevent damage at motion limits.

Example(s) of Measurement

The following are examples of the measurements from the PACDEX flights. These two plots are from the flight of May 23 2007, the red trace from an ice cloud at 1545 UTC and the blue trace from a water cloud at 2048 UTC. The top plot shows measured irradiance and the bottom plot normalizes the two irradiances to emphasize how the absorption features reveal the water-phase of the clouds.

The following panel is a sample of data from the actinic flux portion (CAFS) of HARP. Here the downwelling component of actinic flux from three separate flights are plotted together with the flux calculated from the Troposphere UV and Visible (TUV) model developed at NCAR: