commerce logo          U.S. DEPARTMENT OF COMMERCE
                                                        National Oceanic and Atmospheric Administration
                                                       NATIONAL WEATHER SERVICE
                                                        Silver Spring, Md. 20910

                                                        May 6, 1991                                         W/OH2
 
 

TO:               All Holders of Operations Manual
SUBJECT:    Transmittal Memorandum for Operations Manual Issuance 91-4

1.    Material Transmitted: WSOM Chapter E-31, National Operational Hydrologic Remote Sensing Center.

2.    Summary:

This revised chapter defines the management structure for the Center which includes the consolidation of the Airborne Snow Survey Program and the Satellite Snow Cover Mapping Program. Interagency support and remote sensing schedules have been updated.

3.    Effect on Other Instructions:

WSOM Part E has been restructured. The next Table of Contents/Inventory to be issued will provide two listings for Part E. The restructured Part E listing will show current chapters in parentheses, and the dates shown will be those of existing chapters. The other listing will contain the information as it now exists.

This WSOM Chapter E-31 supersedes WSOM Chapter E-21, issuance 84-17, dated November 7, 1984.

Albert W. Friday, Jr.
Assistant Administrator
  for Weather Services


Issue Date     Org. Code        NATIONAL WEATHER SERVICE     Part    Chap.
5-6-91            W/OH2                 Operations Manual                            E        31
 
 

NATIONAL OPERATIONAL HYDROLOGIC REMOTE SENSING CENTER

Table of Contents:

1. Introduction

2. Management

    2.1     Office of Hydrology
    2.2    Regional Offices
    2.3    River Forecast Centers (RFC)
    2.4    Weather Service Forecast Offices (WSFO)

3.    Airborne Gamma Radiation Snow Survey Program

    3.1     Aircraft Operations Center
    3.2    Airborne Snow Survey Schedule
            3.2.1     Scheduled Missions
            3.2.2     Emergency Missions
            3.2.3     Survey Schedule Conflicts

    3.3     Airborne Data Dissemination

4.    Satellite Hydrology Program

    4.1     Satellite Data Collection
    4.2    Satellite Data Dissemination

5.    Publications and Program Information

6.    Transition to the Modernized and Restructured National Weather Service

Exhibits:

E-31-1     Airborne Snow Survey Flight Line Network
E-31-2    1990 Snow Mapping Windows
E-31-3    1990 Snow Mapping Basins


1.     Introduction. The Office of Hydrology of the National Weather Service (NWS) maintains a National Operational Hydrologic Remote Sensing Center (NOHRSC) to generate remotely sensed hydrology products. The NOHRSC uses terrestrial gamma radiation sensed from low-flying aircraft to estimate snow water equivalent over a network of more than 1600 flight lines covering portions of 26 states and 7 Canadian provinces. These flight lines are depicted in Exhibit E-31-1. Additionally, advanced very high resolution radiometer (AVHRR) satellite data are used to digitally map areal extent of snow cover over regions covering two-thirds of the United States and southern Canada where snow cover is a significant hydrologic variable. Areal extent of snow cover windows are depicted in Exhibit E-31-2. The real-time, airborne snow water equivalent data and satellite areal extent of snow cover data are used operationally by the NWS when issuing spring flood outlooks, water supply outlooks, river and flood forecasts, and reservoir inflow forecasts.

Since 1980, the NWS maintained a Satellite Snow Cover Mapping program based in Kansas City. In FY 1987, the Satellite Snow Cover Mapping program was transferred from the National Severe Storms Forecast Center in Kansas City to the Office of Hydrology in Silver Spring. In FY 1988, the Airborne Snow Survey and the Satellite Snow Cover Mapping programs were physically consolidated into the NOHRSC based in Minneapolis, Minnesota.

2.     Management.

2.1     Office of Hydrology. The consolidation of the Airborne Snow Survey program and the Satellite Snow Cover Mapping program constitutes the NOHRSC. The Center is based in Minneapolis. The Director of the NOHRSC reports directly to the Chief of the Hydrologic Operations Division in the Office of Hydrology.

Staff supporting the NOHRSC includes both NWS employees and National Oceanic and Atmospheric Administration (NOAA) Corps commissioned officers. NWS hydrologists and computer programmers support the data collection and analysis requirements of the Center. NOAA Corps commissioned officers serve as program pilots, are assigned to the NOAA Aircraft Operations Center, and are attached to the NOHRSC in Minneapolis. The Office of Hydrology also maintains a NOAA Corps billet for one additional commissioned officer who is assigned to the Center and serves as the deputy.
 



 


The Center's director is responsible for providing status information directly to the Chief, Hydrologic Operations Division, and appropriate regional hydrologists. Status information includes information concerning data collection schedules, airborne and satellite data sets, program accomplishments, and future plans. Various technical and administrative aspects of the Center are discussed in the National Operational Hydrologic Remote Sensing Program User's Guide which is available from the Center upon request. The User's Guide is updated and distributed to all appropriate NWS personnel.

2.2     Regional Offices. The regional hydrologist is responsible for the transmission of all appropriate NOHRSC status information to the regional director and to the appropriate NWS field offices. The regional hydrologist provides guidance to the NOHRSC for airborne and satellite data collection and dissemination activities within the region. Regional support to the NOHRSC shall be requested through the regional hydrologist.

2.3     River Forecast Centers (RFC). The Center's director shall coordinate with the RFCs to develop and maintain an operational airborne and satellite data collection program in their areas of hydrologic responsibility.

2.4     Weather Service Forecast Offices (WSFO). The Center's director shall coordinate with the WSFOs to develop and maintain an operational airborne and satellite data collection program in their Hydrologic Service Areas. The area manager is responsible for the dissemination of NOHRSC data to the public and mass media

3.     Airborne Gamma Radiation Snow Survey Program. Within the NOHRSC, the operational Airborne Gamma Radiation Snow Survey program provides real-time snow water equivalent and soil moisture measurements to support the various NWS operational hydrology programs. The operational field area includes portions of 26 states and 7 Canadian provinces. Airborne snow water equivalent and soil moisture measurements are made over selected flight lines at critical times during the year. Each flight line is approximately 10 miles long and 1,000 feet wide giving a mean areal measure of snow water equivalent or soil moisture over a 2- to 3-square-mile area. The airborne data are reported in near real-time over Automation of Field Operations and Services (AFOS)) in Standard Hydrologic Exchange Format (SHEF) for NWS users and over a commercial electronic bulletin board (MCI Mail) for non-NWS users.

The program uses airborne detection systems and NOAA aircraft maintained by the NOAA Aircraft Operations Center to make over 1,000 airborne snow water equivalent measurements during each snow survey season. Airborne data collection missions are classified as operational, expanded, or research missions. Each of these three categories is, in turn, classified as a background, soil moisture, or snow survey mission. Background radiation data are collected during snow-free periods and used to calibrate a flight line network. Soil moisture missions are typically flown to measure the soil moisture in the upper 20 centimeters of soil in the late fall. Snow survey missions are typically flown between January and April to make airborne snow water equivalent measurements. Operational survey missions are flown primarily to provide support to the hydrology program in the upper Midwest. Expanded or research survey missions are periodically flown in the Eastern and Western Regions (on the expanded flight line network) on an emergency or as-needed basis.

3.1     Aircraft Operations Center. The NOAA Aircraft Operations Center maintains the principal snow survey aircraft which is a twin Aero Commander. The aircraft is based in Minneapolis, Minnesota, and is equipped with a gamma radiation detection package used to measure snow water equivalent. The detector is also used to measure soil moisture content. This aircraft operates in the north-central and northeast United States and Canada. NOAA Corps commissioned officers assigned to the NOHRSC function as airborne survey mission pilots and assist in data analysis and program management duties.

A Turbo Commander has been calibrated to make measurements on the flight line network in the West. A second Aero Commander has been calibrated to serve as a backup aircraft.

3.2     Airborne Snow Survey Schedule.

3.2.1     Scheduled Missions. An airborne survey is typically scheduled for the upper Midwest prior to the week of each spring flood outlook. The Center's director shall coordinate the survey schedule with the appropriate RFCs and WSFOs and shall provide the schedule to the regional hydrologists. Cancellation of scheduled survey missions shall be coordinated with the regional hydrologists, RFCs, and WSFOs.

Other Federal agencies can request airborne snow surveys over existing NWS flight lines. Additionally, other Federal agencies can request that the NOHRSC establish an agency-specific flight line network for special airborne data collection missions. The costs associated with airborne data collection are typically defrayed by the requesting agency. All requests from other Federal agencies for airborne snow survey support are directed to the Center's director and coordinated with the appropriate regional hydrologist and RFC. NWS airborne data collection schedules take priority over airborne data collection schedules requested by other Federal agencies.

3.2.2     Emergency Missions. Nonscheduled or emergency snow surveys are requested by the regional hydrologists or RFCs and coordinated with the WSFOs. Actual emergency survey schedules shall be provided by the Center's director to the regional hydrologists.

3.2.3     Survey Schedule Conflicts. Conflicting schedule requests for an airborne survey between RFCs within a region shall be resolved by the regional hydrologist. Conflicting schedule requests between the regions shall be resolved by the Chief, Hydrologic Operations Division.

3.3     Airborne Data Dissemination. The Center's director is responsible for verifying the quality of the airborne measurements and disseminating the operational data to the appropriate RFCs and WSFOs in near real time over AFOS in SHEF.

4.     Satellite Hydrology Program. Areal extent of snow cover measurements are made using AVHRR data from the NOAA polar orbiting satellites. The NOHRSC is responsible for generating and disseminating remotely sensed hydrology products derived from satellite data. Satellite hydrology products include areal extent of snow cover for all major river basins in the United States and southern Canada where seasonal snow cover is a significant hydrologic variable. In the western United States, areal extent of snow cover is estimated for as many as five elevation zones for each basin, and percentage of snow cover is reported for each elevation zone.

Digital image processing techniques have been developed by the NWS, Bureau of Reclamation, and the U.S. Geological Survey for use by the NOHRSC to generate areal extent of snow cover maps in near real time using georegistered AVHRR image data. Methods have been developed to classify AVHRR images into snow cover, cloud cover, snow and cloud amounts, and snow in trees and open areas.

The classified AVHRR images are transmitted to a geographic information system where digital elevation model data and basin boundary information are used to calculate the percentage of snow cover, by elevation zone, for each of the basins of interest in the AVHRR scene. Both multidate change-detection and single-date multispectral image classification procedures have been developed and used for operational snow cover mapping.

4.1     Satellite Data Collection. The regional hydrologists provide guidance to the NOHRSC for satellite data collection activities within the regions. Basins are identified for satellite snow cover mapping by staff at the RFCs and WSFOs (see Exhibit E-31-3). Satellite snow cover mapping typically begins in January of each year and continues through June or July in regions of the country where snow cover remains. The program attempts to produce a snow cover map for each basin of interest in the country approximately once a week. Cloud cover, however, obscures the satellite sensing and, consequently, cloud-free images are not always available once each week.

4.2     Satellite Data Dissemination. The areal extent of snow cover data, by elevation zone, is posted to a commercial electronic bulletin board (MCI Mail) in SHEF approximately 36 hours after the satellite overpass. Because of the excessive length of this alphanumeric product, it is not sent on AFOS. Rather, the snow cover window number and date of the snow cover man are distributed over AFOS at the time of MCI Mail posting.

The NOHRSC also produces digital images of snow cover classification for the entire AVHRR scene or for specific basins within a scene. The digital images are used by end-users who have the capability of manipulating the imagery in a digital image processing or geographic information system environment.

5.     Publications and Program Information. Details of the airborne and satellite snow measurement techniques and the associated data analysis and distribution procedures are discussed in the National Operational Hydrologic Remote Sensing Program User's Guide. Program publications, progress reports, publication listings, and the User's Guide are available from:

NOAA, National Weather Service
Office of Hydrology
National Operational Hydrologic Remote Sensing Center
6301 34th Avenue South
Minneapolis, Minnesota 55450

6.     Transition to the Modernized and Restructured National Weather Service. The management, design, and guidance of the National Operational Hydrologic Remote Sensing program outlined in this chapter shall be valid through Stage I of the modernized and associated restructuring (MAR) of the NWS. Stage I is defined as the period of operations of new WSFOs and WSOs. During Stage I, the NOHRSC will begin to use information from the deployed advanced Doppler weather surveillance radar systems for estimating snowfall amounts.

During Stage I, this chapter will be amended by means of an OML or will be reissued to reflect program changes after Stage I of the MAR.


WSOM Issuance
91-4    5- 6-91