Operational Space Environment Network Display (OpSEND)

Authors


Abstract

[1] The Air Force Research Laboratory and Space and Missile Systems Center, Detachment 11, have implemented a new system of graphical products that provide easy-to-visualize displays of space weather effects on various radio systems operating through the ionosphere. By means of a three-level Web page, the user can select the radio system (UHF, HF, GPS, or radar), the map area (global or regional theater where the radio system is located), the time (nowcast or forecast), and additional options. This system, the Operational Space Environment Network Display (OpSEND), was first installed at the 55th Space Weather Squadron, Schriever Air Force Base (AFB), Colorado, and is now producing its first four products with a new Web format at the Air Force Weather Agency, Offutt AFB, Nebraska. Radar auroral clutter maps specify (nowcast) the estimated position and strength of the auroral oval relative to radar coverage regions. UHF Satcom scintillation maps nowcast and 2-hour forecast ionospheric scintillation and its potential degradation to UHF Satcom communication links. HF illumination maps nowcast and 1-hour forecast HF communication performance. Estimated GPS single-frequency error maps nowcast and 1-hour forecast positioning errors resulting from GPS constellation geometry and inaccurate ionospheric correction. Details and examples are presented.

1. Introduction

[2] The space environment affects the function of multiple Department of Defense (DOD) systems, including UHF satellite communications, GPS navigation, space surveillance radars, and HF radio wave propagation. On 20 January 2000, increment 1 of the Operational Space Environment Network Display (OpSEND), consisting of the prototype UHF and radar products, became operational at the 55th Space Weather Squadron (55SWXS), Schriever Air Force Base (AFB), Colorado. The remaining two products began operation in April 2000. Air Force Research Laboratory (AFRL) Space Vehicles Directorate (VS) supported Space and Missile Systems Center (SMC) Detachment 11 (Det 11) in making the transition to operations using the rapid prototyping facilities located in the Centralized Integrated Support Facility at Colorado Springs, Colorado. OpSEND generates graphical space weather maps, which allow operational users to easily visualize where and to what extent a specific system may be affected. OpSEND is a joint AFRL-SMC program, which builds off the successful Air Force Space BattleLab Space Environment Network Display (SEND) demonstration. OpSEND integrates sensor data, models, and display tools to meet the DOD space weather specification needs for communication, navigation, surveillance, and signal intelligence (SIGINT). The OpSEND products now being generated, and their principal investigators, are: (1) UHF satellite communications scintillation maps (K. Groves), (2) space surveillance radar auroral clutter maps (S. Quigley), (3) single frequency GPS navigation error maps (P. Doherty), and (4) HF illumination maps (T. Bullett).

[3] These products (except the radar product) provide both a nowcast and a 1-hour forecast (2 for UHF). OpSEND products are available to users in near-real time (less than half an hour) at an Air Force Weather Agency (AFWA) network site. Further information may be obtained from AFWA current requirements (AFWA/XORC) at 402-294-1399.

2. OpSEND System

[4] Figure 1 shows a simple block diagram of the components of operational space weather. The process begins with sensors, whether ground-based instruments or satelliteborne technology, that measure space weather parameters in real time. These are analogous to our familiar parameters of temperature, pressure, and wind velocity in tropospheric weather. Data quality control is a key issue. An OpSEND validation study is being conducted which will address product performance and provide a basis for real-time data quality enhancements and performance metrics. Many more sensors are needed to provide detailed updates. Communication from the sensors is a critical link. Ground-based sensors require a rapid return link. This is an issue for many remote sensors. Communication from space requires both special monitor stations and the rapid return link. Communication availability, speed, and quality are key issues.

Figure 1.

OpSEND system overview.

[5] Computer models of the ionosphere and the space environment are located at a central or in-theater processing site. These models are continuously updated by the sensor measurement data. Product drivers then generate impact maps and other products for communication, navigation, surveillance, and other DOD operational systems, by accessing this modeled space environment. Products are then delivered by real-time communication links to in-theater operational users. In the initial OpSEND implementation these products were generated at the 55th Space Weather Squadron, Schriever AFB, Colorado, and distributed electronically.

[6] In the initial implementation of OpSEND, shown in Figure 2, measurements from several sensor sources are used. These include: electron density information from ionosondes, total electron content information from GPS monitors, ionospheric scintillation measurements, magnetic measurements, and measurements from the DMSP satellites. These measurements are now transmitted to AFWA, where they are used to update several space environment models. These models include: the Parameterized Real-Time Ionospheric Specification Model (PRISM; Daniell et al. [1995]), a model of the auroral oval, and the Scintillation Network Decision Aid (SCINDA; Caton et al. [1999]) model. Various codes use the space environment specification provided by these models as input for generation of OpSEND maps that are specific to communication, navigation, surveillance, and HF radio systems. The map products are distributed electronically to support operational users, such as: (1) early warning radars (EWRs); (2) HF radio communication (HF Comm), over-the-horizon (OTH) radar, and SIGINT; (3) GPS and GPS control; and (4) UHF Satcom. Each map product consists of a three-level Web page as follows: (1) map of the world showing theaters or HF transmitters that may be selected; (2) thumbnail maps showing in-theater choices, including nowcast versus forecast; and (3) enlarged theater space environment impact map selected at level 2.

Figure 2.

OpSEND system architecture detail.

2.1. OpSEND Product: UHF Satcom Scintillation Map

[7] Ionospheric scintillation is a noise-like effect on radio signals caused by their passing through disturbed regions of the ionosphere. These disturbances occur at times in certain regions of the globe. Although it is currently possible to state the likelihood of occurrence at a specific time/place, these disturbances cannot yet be specifically predicted. Thus it is useful to monitor and detect their occurrence and to display their effects in real time. Figure 3 shows the OpSEND UHF Satcom scintillation map product [Groves et al., 1997] with its three Web page levels:

Figure 3.

UHF Satcom scintillation map product; three-level Web page.

[8] 1. The first level displays the global theater options that may be selected. Global subregions may be selected which display theaters such as U.S. Pacific Command (PACOM), U.S. Southern Command (SOUTHCOM), and U.S. European Command (EUCOM), (theaters defined by commands, not space weather regions). It should be noted that the UHF scintillation regions that are mapped show only the strong scintillation effects that can occur within approximately 30 degrees latitude of Earth's geomagnetic equator. Weaker scintillation effects occur in the high-latitude regions, but these are not yet displayed.

[9] 2. The second level displays thumbnail maps of available in-theater choices. The user may choose a nowcast or a 2-hour forecast map (forecast derived from observed feature width and observed or modeled drift velocity). The user may also choose among maps that show scintillation effects from the perspective of different UHF communication satellites that are visible from the chosen theater.

[10] 3. The core level enlarges the map selected by the user on level 2. Here the colored area shows where scintillation would be observed in-theater by a ground-based user monitoring the selected satellite. The (red/yellow/green) colors indicate the strength of the scintillation according to preset thresholds. In effect, the colored area may be thought of as the satellite radio transmission “shadow” cast on the ground by the ionospheric region causing the scintillation. In this example, there is only one scintillation region; there are often many such regions, especially by late evening times. A single sensor is sufficient to detect the regions and support this map, although more sensors are clearly desirable.

2.2. OpSEND Product: HF Illumination Map

[11] The HF illumination map is a new AFRL-developed concept that displays the amount of HF radio energy reaching every part of a chosen theater from a specified HF transmitter. This radio energy reaches a given point in-theater by being reflected from the ionosphere (as AM radio does at night). In some parts of the theater, “multiple hop” reflections are needed. When the ionosphere has low densities or rapid geographic changes, it is sometimes not physically possible to reach portions of the theater with a particular chosen frequency. Figure 4 shows the OpSEND HF illumination map product with its three Web page levels:

Figure 4.

HF illumination map product, three-level Web page.

[12] 1. The first level displays a global map with locations of specific HF transmitter sites. These may be selected (“clicked”) by the user to display maps.

[13] 2. The second level displays thumbnail maps of available in-theater choices. The user may choose a nowcast or a 1-hour (PRISM-derived) forecast map. The user may also choose among maps that show HF illumination for specific frequencies available for the chosen transmitter. Choice of frequency often dramatically alters the distribution of HF illumination over the theater.

[14] 3. The core level enlarges the map selected by the user on level 2. Here the colors indicate the strength of HF illumination available in each sector of the chosen theater for the chosen transmitter and frequency.

2.3. OpSEND Product: Radar Auroral Clutter Map

[15] The radar auroral clutter map displays the current position of the “auroral oval,” a high-latitude region where charged particles may precipitate down along Earth's magnetic field and disturb the ionosphere (Figure 5). The auroral oval is shown with respect to the coverage fan of a selected ground-based space surveillance radar. More specifically, the region where the chosen radar may look perpendicular to the magnetic field is indicated (turquoise loop) since only in this region could radar energy be reflected back with enough strength to cause clutter. When space environment conditions cause the auroral oval to intersect the “turquoise loop,” then auroral clutter is possible, although nonuniformities in the auroral conditions may prevent clutter occurrence. When the auroral oval does not intersect the “turquoise loop,” then radar auroral clutter is not likely. OpSEND radar auroral clutter map product three Web page levels are (Figure 5):

Figure 5.

Radar auroral clutter map product, three-level Web page.

[16] 1. The first level displays a global map with locations of specific radar sites. These may be selected (“clicked”) by the user to display maps.

[17] 2. The second level displays thumbnail maps of available in-theater choices. The user may choose a nowcast or a 1-hour forecast map (forecast not yet implemented). The user may also choose among maps that show horizontal and vertical clutter profiles.

[18] 3. The core level enlarges the map selected by the user on level 2. Here the colors indicate the strength of the auroral electron flux, which correlates to the likelihood of clutter occurrence in the region perpendicular to the magnetic field.

2.4. OpSEND Product: GPS Single-Frequency Error Map

[19] The GPS single-frequency error map displays the navigation position errors in a chosen theater for users of single-frequency GPS receivers. These receivers (which are the vast majority of civilian units but are now less used by military) use a simple built-in algorithm to correct for ionospheric errors. This algorithm only corrects for about 50% of those navigation errors. The impact of this limited correction is found by comparison with a more accurate correction derived from a real-time model of the ionosphere (PRISM), updated by GPS TEC sensor data and global Kp. The map shows the combined effect of the limited built-in ionospheric correction and GPS satellite geometry at the moment as seen from each point in theater. Figure 6 shows the OpSEND GPS single-frequency error map product [Smitham et al., 1999] with its three Web page levels:

Figure 6.

GPS single-frequency error map product, three-level Web page.

[20] 1. The first level displays the global theater options that may be selected. Global subregions may be selected which display theaters such as PACOM, SOUTHCOM, and EUCOM. A global map may also be selected.

[21] 2. The second level displays thumbnail maps of available in-theater choices. The user may choose a nowcast or a 1-hour (PRISM-derived) forecast map. The user may also choose between maps of errors from flat or “hilly” terrain. Hilly terrain is estimated by blocking access to satellites below a 15 degrees elevation angle, to simulate obstruction, whereas flat terrain is simulated via a 5 degree cutoff. At this level the user may also choose among display of horizontal error, altitude error, and total position error.

[22] 3. The core level enlarges the map selected by the user on level 2. Here the colors indicate the magnitude of the position error in meters.

3. OpSEND Product Examples

[23] Several additional examples are provided to illustrate the character and variation of the OpSEND Products. Figure 7 presents a more current version of the UHF Satcom scintillation map product. Figure 8 shows an example of diurnal variation of the HF illumination map product in one region. Figure 9 illustrates variation of the radar auroral clutter map product with Kp variation (for a nonexistent radar), and Figure 10 gives a global example of diurnal variation of the GPS single-frequency error map product.

Figure 7.

Current UHF Satcom scintillation map.

Figure 8.

Example diurnal HF illumination maps, signal-to-noise ration, Croughton, UK, 4.5 MHz, 21 October 1999, 09:00 UT, to 22 October 1999, 05:00 UT.

Figure 9.

Variation of the radar auroral clutter map product with Kp variation.

Figure 10.

Example GPS single-frequency error maps, global, flat terrain, three-dimensional (latitude/longitude/altitude). Error, 21 October 1999, 09:00 UT, to 22 October 1999, 05:00 UT.

4. Summary

[24] The OpSEND system is now producing its first four products at the AFWA, Offutt AFB, Omaha, Nebraska. This multilevel Web-based system of graphical products provides easy-to-visualize displays of space weather effects on various radio systems operating through the ionosphere. Nowcasts, and a 1-hour (GPS and HF) or 2-hour (UHF) forecast, are available to users in near-real time at an AFWA network site. The four products are: UHF Satcom scintillation maps, radar auroral clutter maps, HF illumination maps, and GPS single-frequency error maps.

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