Disdrometer_Statement_of_Work.pdf

Statement of Work

Disdrometer Procurement

Dr. Michelle Zeisset

Phone: (575) 679-1937 E-mail address: michelle.zeisset@us.af.mil

846 Test Squadron Holloman Air Force Base, NM

Contract/Project Number: TBD

Revision Date: 12 Apr 18

DISTRIBUTION A. Approved for public release: distribution unlimited.

DISTRIBUTION A – APPROVED FOR PUBLIC RELEASE

1.0 BACKGROUND

The Holloman High Speed Test Track (HHSTT) is responsible for conducting weather effects testing in the simulated rain environments produced along the length of the track. The simulated environment must be characterized and controlled to assure test customers that their test item is being exposed to a known, predictable, and reproducible rain environment. A disdrometer is a system that measures the rain drop size distribution (DSD) of a given spray, and in so doing provides the ability to characterize the DSD produced both in the HHSTT rain lab and by the rainfield.

2.0 SCOPE

The scope of this effort is to procure a disdrometer that will be used to make laboratory and field DSD measurements of the simulated rain environments at the HHSTT. The disdrometer system shall be made to meet the minimum characteristics and specifications outlined in Section 3.0. This integrated system shall include all hardware and software, if any, required to operate the system.

3.0 TECHNICAL REQUIREMENTS

Disdrometer requirements are summarized in Table 1. Each requirement is assigned a criticality level of either 1 or 2, representing non-negotiable (i.e., mandatory) and negotiable (i.e., not mandatory) requirements, respectively. Several of the non-negotiable requirements are discussed in further detail in the following sections.

Table 1. Disdrometer Requirements

Requirement Criticality

Level Values Justification

Droplet diameter measurements across range of interest

1 0.2 – 6.0 mm DSD is the single most critical measurement required of this device

Droplet diameter resolution 1 ± 0.1 mm

Droplet diameter accuracy 1 ≤ 20% error

Accurate measurements in winds up to 10 kts

The device will be used in experiments that examine how wind affects the DSD

Number density calculation 1 DSD in N(D) units is the primary parameter of interest that will be compared to rainfield performance specifications

Liquid water content calculation 1 0.005 – 5 g/m3 LWC is a parameter of primary interest;

suggested error limit ± 15%

Must fit within lab and rainfield test space[1]

DSD measurements are only valid in the volume of space occupied by a sled-mounted test article

Must be capable of static and dynamic measurements in the lab and on the rainfield[2]

1 0 – 33 ft/sec

Static measurements provide a link to historical data; dynamic measurements will be used to develop new DSD, validate the final rainfield, and for test day DSD verification; must allow remote control of data collection start and stop

Reasonable sample time 1 The device must be able to obtain enough data in a sparse spray to provide a stable DSD estimate within 60 min; shorter is better

Packaged for outdoor application

The device must withstand dynamic measurement conditions in the rainfield environment

Turnkey HW/SW 1 No additional third party HW or SW is required to perform basic functions (operation, data acquisition and analysis)

Personalized technical support 1 The device remain operational in the unique environments of the HHSTT

Delivery date 1 The device must be delivered in less than 120 days after contract award, i.e., it doesn’t require extensive or long-term R&D

Droplet velocity measurement 2

0.05 - 10 m/s

Provides the ability to determine how closely the simulated rain approaches terminal velocity, this may be an assumption for some disdrometers; suggested accuracy of ± 0.01 m/s

Can resolve overlapping drops 2 Reduces measurement bias

Volumetric rain rate measurement

1 – 5 in/hr

Can be used as a secondary LWC measurement; suggested error limit ± 10%

On-site training 2

[1] If the device doesn’t fit within the test space as is, it may still be considered for purchase if configuration changes to either the device or the lab/rainfield are considered reasonable in terms of cost and schedule.

[2] Dynamic measurements are those made while the disdrometer is moving along the track at velocities up to 10 m/s.

3.1 Measurement Capabilities

3.1.1 Droplet Diameter

The system shall be capable of measuring the diameter of each droplet that passes through the measurement area, including partial drops, with a resolution of 0.1 mm and an accuracy of ≤ 20% error, over the range of 0.2 - 6.0 mm inclusive. Moreover, the device must be capable of taking measurements in winds up to 10 kts without degradation of measurement accuracy and without having to re-orient the device with respect to wind direction.

3.1.2 Static and Dynamic Measurements

The system shall be capable of making accurate measurements in both static (not moving) and dynamic

(moving with constant velocity) modes of operation. Static measurements may require data to be taken over long periods of time (up to several hours), so the system shall be capable of sensing, processing, and storing the measured data for these long duration tests.

The system must be capable of making accurate measurements when moving with respect to the rail at velocities in the range of 0.25 to 33 ft/sec. To support dynamic measurements, the system must allow remote start and stop of data collection. Additionally, the output data files must include time-tagging with sufficient resolution and accuracy that would allow the disdrometer position to be correlated with time.

3.1.3 Measurement Space

The physical space in which the device must take measurements is constrained in the vertical direction by the rail and in the lateral direction by the risers that support the spray nozzles. The system shall be capable of making accurate measurements within the physical measurement space defined in Figure 1.

The discussion in this section refers specifically to the physical dimensions of the system. Placement of the system will be accomplished by HHSTT.

Figure 1. Measurement Space, View Looking North.

Specifically, the system shall be capable of making both static and dynamic measurements within the constrained space of the HHSTT rainfield with the system pointing either northward or southward. The physical space is an 18 inch diameter cylinder that is centered vertically at thirteen inches above the rail and laterally with the centerline of the rail. Horizontal and vertical coordinates are described below as buttline (BL), the lateral deviation in inches from the centerline of the rail and waterline (WL), the vertical deviation in inches from the top of the rail. Westward and eastward deviations from BL = 0 are positive and negative, respectively.

Position A. BL = 0.0 inches, WL = 4.0 inches. The dimensions of the system must be such that it is capable of making measurements at a vertical distance of ≤ 4 inches above the rail without interfering with the rail.

Position B. BL = 9 inches (positioned in the direction of the risers), WL = 13 inches. With the center of the disdrometer sensor area placed at this location, no part of the system shall extend more than 12 inches in the direction of the risers so as not to interfere with the risers (see Figure 1).

Position C. BL = 0 inches, WL = 22 inches. No spatial requirements other than non-interference with track-side infrastructure.

Position D. BL = –9 inches (positioned in the direction opposite from the risers), WL = 13 inches, static and dynamic measurements. No spatial requirement other than non-interference with track-side infrastructure.

All positions within the test space. The disdrometer shall be capable of making accurate measurements anywhere within the interior of the 18-inch diameter test space.

18" diameter

13"

Measurement Space

A

B

C

D

3.2 Computational Capability

3.2.1. Number Density

Number density is defined as the expected number of drops per unit volume at any instant in time, reported as drops/m3. The system shall be capable of computing an unbiased estimate of number density based upon the measured droplet diameters in near real-time. The system shall provide the number density in user-selectable drop diameter bin sizes, as well as providing time-tagged output data files that will allow user post-processing.

3.2.2. Liquid Water Content

Liquid water content is defined as the mass of water per unit volume at any instant in time, reported as g/m3. The system shall be capable of computing liquid water content based upon the measured droplet diameters in near real-time. The system shall provide liquid water content values in user-selectable drop diameter bin sizes, as well as providing time-tagged output data files that will allow user post-processing.

3.2.3. Sampling Efficiencies

The sprays produced by the HHSTT are intended to replicate gamma-based natural rain DSD. Hence, they are sparse sprays with the largest drops being relatively rare. Past data collection efforts on the

HHSTT rainfield required between 60,000 and 100,000 observed drops to achieve a stable DSD estimate, which can take an unreasonable amount of data collection time if the sensor area is too small. Hence, the system shall implement measures such that the time required to achieve an unbiased and stable estimate of the DSD is reasonable, preferably ≤ 60 minutes per sample. Some of these measures may include, but are not necessarily limited to:

Expanding the sensing area to the greatest extent possible while maintaining the required diameter measurement resolution and system size constraints.

The system shall have the option to record and process frames that contain a drop or a portion of a drop and discard frames that do not contain an image.

The system shall compensate for partial drops, or images that don’t contain the entire drop but a portion of it (i.e., edge drops).

o To improve data collection efficiency, the processing algorithm shall be capable of estimating the diameter of the edge drop.

o To ensure an unbiased estimate of number density, the processing algorithm shall implement measures that properly compensate for changes in the effective measurement area (or volume) due to the acceptance, rejection or other treatment of edge drops.

3.3 Environmental Factors

3.3.1 Field Operation

The system shall be capable of sustained operation in an outdoor rain environment under both dynamic and static conditions. All critical sensors and electronic components, interconnecting cables, and connectors shall be packaged such that operation is not adversely impacted by the operational environment:

Vibration and shock loads during operation as the device traverses along a steel crane rail at speeds up to 33 ft/sec, with acceleration up to ± 2 g parallel to the rail.

Operating temperatures between 32° F and 104° F.

Vibration and shock loads during handling to and from a storage rack; transport in the bed of a pickup truck over improved roads; and installation onto and removal from a rail cart.

3.3.2 Transportation and Storage

The system shall be housed in a container that will protect it during shipping, storage and transport. This container will be used to store the components during extended periods of non-use, and to transport the system to and from storage to the lab or the rainfield, and to different locations along the rainfield in the bed of standard pickup truck with no special provisions for shock or vibration isolation.

4.0 Deliverables

All deliverables shall be completed within four months of award in order to meet the needs of a specific mission:

Fully operational turn-key system.

Transportation and storage container.

Interconnect cables that carry power, control commands, and data between the system sub-components.

Operating and maintenance manuals; theory of operation manual.

On-site training covering set-up, calibration and operation and maintenance of the system.

Continuing technical support for a period of two years or until the completion of the HHSTT rainfield characterization effort, whichever occurs first.

A mutually agreed upon calibration plan, submitted for government approval prior to execution.

A mutually agreed upon system test plan, submitted for government approval prior to execution.

Execution of the test plan will be witnessed at the discretion of the government.

Calibration documentation, including a report and data, traceable to National Institute of Standards and

Technology (NIST) or other mutually agreed upon standards.

Suggested calibration and maintenance support plan including pricing for future calibration.

5.0 Shipping

The system will be shipped to:

846th Test Squadron

1521 Test Track Road

Holloman AFB, NM 88330

Attn: Dr. Michelle Zeisset

DISTRIBUTION A. Approved for public release: distribution unlimited.