User Request Guidelines - PRISM & AVNIR-2 -


Background
The ALOS mission features a systematic observation strategy which comprises pre-launch, systematic global observation plans for all three instruments. The strategy is implemented as a top-level foreground mission and with a priority level second only to that of emergency observations.

Users of all categories (scientific and commercial users, ALOS Principal Investigators, etc.) who wish to place additional observation requests for ALOS data (via the regional ALOS Data Nodes) are strongly encouraged to align new observation requests with the JAXA observation strategy in order to avoid programming conflicts and thereby to improve individual request success rates.

PRISM Strategy Characteristics
The default mode for PRISM is the triplet mode, which allows simultaneous along-track stereo observations with the three telescopes. As the swath width in triplet mode however is reduced to 35 km, PRISM requires two 46-days cycles to cover a given region without gaps, during which the instrument is alternately tilted 1.2° across-track to the right and left. In regions above

AVNIR-2 Strategy Characteristics
The default mode for the AVNIR-2 scenario observations is the nadir view mode, as indicated in the table below.

For any given region, AVNIR-2 is typically scheduled for "one acquisition during two consecutive cycles", meaning that if an acquisition is successfully programmed the first of the two cycles in question, it will not be included in the plan during the second (regardless of cloudcover). One full global AVNIR-2 coverage is planned per year as a part of the observation strategy.

As the AVNIR-2 instrument however operates with only half the data rate of that of PRISM and PALSAR, there is comparably favourable opportunities for users to make additional requests for AVNIR-2.

PRISM and AVNIR-2 operational default modes per cycle
Cycle # Start date PRISM AVNIR-2
1 Commissioning Commissioning
2
3 19-Apr-06 Cal / Val Cal / Val
4 4-Jun-06
5 20-Jul-06
6 4-Sep-06
7 20-Oct-06 +1.2° Nadir
8 5-Dec-06 -1.2° Nadir
9 20-Jan-07 +1.2° Nadir
10 7-Mar-07 -1.2° Nadir
11 22-Apr-07 +1.2° Nadir
12 7-Jun-07 -1.2° Nadir
13 23-Jul-07 +1.2° Nadir
14 7-Sep-07 -1.2° Nadir
15 23-Oct-07 +1.2° Nadir
16 8-Dec-07 -1.2° Nadir
17 23-Jan-08 +1.2° Nadir
18 9-Mar-08 -1.2° Nadir
19 24-Apr-08 +1.2° Nadir
20 9-Jun-08 -1.2° Nadir
21 25-Jul-08 +1.2° Nadir
22 9-Sep-08 -1.2° Nadir
23 25-Oct-08 +1.2° Nadir
24 10-Dec-08 -1.2° Nadir
25 25-Jan-09 +1.2° Nadir
26 12-Mar-09 -1.2° Nadir
27 27-Apr-09 +1.2° Nadir
28 12-Jun-09 -1.2° Nadir
29 28-Jul-09 +1.2° Nadir
30 12-Sep-09 -1.2° Nadir
31 28-Oct-09 +1.2° Nadir
32 13-Dec-09 +1.2° Nadir
33 28-Jan-10 -1.2° Nadir
34 15-Mar-10 +1.2° Nadir
35 30-Apr-10 -1.2° Nadir
36 15-Jun-10 +1.2° Nadir
37 31-Jul-10 -1.2° Nadir
38 15-Sep-10 +1.2° Nadir
39 31-Oct-10 -1.2° Nadir
40 16-Dec-10 +1.2° Nadir
41 31-Jan-11 -1.2° Nadir
42 18-Mar-11 +1.2° Nadir
43 3-May-11 -1.2° Nadir

For detailed overviews of which specific regions that are programmed for acquisition during a given cycle for the two instruments, click on the links below:

User Guidelines
Users of all categories (scientific and commercial users, ALOS Principal Investigators, etc.) who consider making additional observation requests for ALOS data (via the regional ALOS Data Nodes) are strongly encouraged to align new observation requests with the JAXA observation strategy in order to avoid programming conflicts. As the observation strategy is implemented with higher priority than general user requests, alignment will also result in improved individual request success rates.

In order to take advantage of existing acquisitions already planned within the observation strategy, and to avoid introducing conflicting requests, please go through the simple procedure below:

Step 1. Check whether your area of interest is already scheduled for acquisition.

  • Find out the cycle number for your preferred time period in the table above. For PRISM, take note of the prevailing tilting direction.
  • Consult the PRISM or AVNIR-2 cycle plots to determine whether your area already is scheduled during the cycle in question.

Step 2, Case 1 (PRISM). Your area of interest is scheduled by PRISM

  • No action is required from your side. The area is scheduled for acquisition with the default mode indicated for the cycle in question.
  • Requests for acquisitions with a sensor mode deviating from the prevailing default mode will be rejected.

Step 2, Case 2 (AVNIR-2). Your area of interest is scheduled by AVNIR-2

  • You are recommended to submit a new acquisition request (nadir viewing) for safety (the AVNIR-2 plan is based on 1 observation in 2 cycles and it is not evident during which of the two cycles indicated that the acquisition will take place).
  • Requests for acquisitions with a sensor mode other than nadir will be rejected.

Step 2, Case 3. Your area of interest is not scheduled.

  • You need to submit a new acquisition request. For PRISM, you must request the default sensor mode indicated in the table for the cycle in question.
  • AVNIR-2 requests at nadir viewing are recommended, although this is not an absolute requirement.

Step 2, Case 4. You are unsure whether your area of interest is scheduled; it is located close to the border of a scheduled and non-scheduled region.

  • You are recommended to submit a new acquisition request, keeping to the default sensor mode for the cycle in question.
  • Requests for acquisitions with a sensor mode deviating from the prevailing default mode will be rejected.

Miscellaneous information

  • ALOS completes 671 orbits during a 46-day satellite cycle
  • 8 satellite cycles per year (368 days)
  • Cycle 1-2: Commissioning phase
  • Cycle 3-6: Calibration/Validation phase
  • Cycle 7+: Operational acqusitions according to the Observation Strategy
  • The estimated average success rate for PRISM and AVNIR-2 acquisitions planned within the observation strategy is about 75% and 80%, respectively.